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4
Fractions
CHAPTER
4.1 Fractions revision 2 7 2 7
of this circle is shaded. is a fraction.
The top number shows that 2 parts of the circle are shaded The bottom number shows that the circle is divided into 7 equal parts
2 7
The top number of the fraction is called the numerator The bottom number of the fraction is called the denominator
Equivalent fractions are fractions that are equal. If both the numerator and the denominator of a fraction are multiplied by the same number then an equivalent fraction is obtained.
1 2 3 6
2
3
2 1 3 6
3 1 3 9
2
3
3 9
and are all equivalent fractions.
A fraction can be simplified if the numerator and denominator can both be divided by the same number. This process is called cancelling. 2
7
3 6 20 10
3 21 35 5
2
7
When a fraction cannot be simplified, it is in its simplest form or in its lowest terms.
Example 1 Find the simplest form of 1380
Solution 1 6 is the highest common factor of 18 and 30 Divide both 18 and 30 by 6 The simplest form of 1380 is 35
6
3 18 30 5 6
Fractions sometimes have to be put in order of size. To do this when fractions have the same denominator, compare the numerators. 53
Fractions
CHAPTER 4
When fractions have different denominators: ● find the lowest common denominator (lowest common multiple of the denominators) ● change each fraction to its equivalent fraction with this denominator ● compare the numerators to put the fractions in order.
Example 2 Write the fractions 14 120 and 25 in order of size. Start with the smallest fraction.
Solution 2 The lowest common denominator for the three fractions is 20 Equivalent fractions for each of 14 120 and 25 with a denominator of 20 are 5
2
4
5 1 4 20
4 2 10 20
8 2 5 20
5
2
4
Starting with the smallest fraction, the order is that is
4 20 2 10
5 20 1 4
8 20 2 5
An improper fraction is one in which the numerator is greater than the denominator. For example, 54 152 and 184 are improper fractions. The improper fraction 54 can be thought of as ‘5 over 4’ or as 5 quarters. Similarly, the improper fraction 152 can be thought of as ‘12 over 5’ or as 12 fifths. A mixed number consists of a whole number and a fraction. For example, 234 315 and 678 are mixed numbers. Mixed numbers can be changed to improper fractions and vice versa. For example, to change 234 to an improper fraction, work out how many quarters there are in 234 There are 4 quarters in 1 and so there are 8 (2 4) quarters in 2 Add the extra 3 quarters to get 11 quarters. So
234 141
(2 4) 3 11 234 4 4
To change the improper fraction 167 to a mixed number, firstly work out how many whole ones there are. 6 sixths is 1; 12 sixths is 2 and so 17 sixths is 2 whole ones and 5 sixths. 1 7 6
256
17 6 2 remainder 5 2 is the whole number 5 is the fraction 6
Exercise 4A 1 Copy the fractions and fill in the missing number to make the fractions equivalent. b 27 4 c 23 15 d 35 12 a 15 10 3 4 5 15 7 e 8 32 f 9 45 g 6 h 8 28 2 Copy the fractions and fill in the missing number to make the fractions equivalent. b 58 48 c 29 54 d 35 24 a 47 28 21 15 5 7 3 7 e 12 36 f 20 g 16 h 25 100
54
4.2 Addition and subtraction of fractions
CHAPTER 4
3 Write each fraction in its simplest form. b 68 c 271 d a 36
1 0 40
e
2 0 25
f
1 2 16
g
4 2 48
h
3 6 40
4 Write each fraction in its simplest form. 0 0 2 5 b 2540 c 1 d a 150 100
7 5 200
e
4 8 60
f
7 2 90
g
8 5 100
h
12 5 1000
d h
9 4 3 20 5 4 1 1 1 7 3 5 2 5 12 30 15
5 Write each set of fractions in order. Start with the smallest fraction. b 56 34 c 23 56 172 a 35 170 e 145 13 130 f 34 196 58 g 2430 170 35 1230 6 Julie and Susan have identical chocolate bars. Julie eats 34 of her chocolate bar. Susan eats 78 of her chocolate bar. Who eats more chocolate? Give a reason for your answer. 7 Ahmid says that 172 is bigger than 56 because 7 is bigger than 5 Is Ahmid correct? You must give a reason for your answer. 8 Change these mixed numbers to improper fractions. b 135 c 216 d 278 a 112
e 434
9 Change these improper fractions to mixed numbers. b 43 c 149 d a 75
e
1 4 5
f 625
2 7 5
f
3 0 7
4.2 Addition and subtraction of fractions 3 5
of the rectangle is shaded red and 15 of the rectangle is shaded green. 4 of the rectangle is shaded. 5 So
3 5
15 45
3 5
1 5
4 5
To add fractions with the same denominator, add the numerators but do not change the denominator. For example, 49 29 69 which in its simplest form is 23 To add fractions with different denominators, firstly find the lowest common denominator and then change each fraction to its equivalent fraction with this denominator.
Example 3 Work out 23 15
Solution 3 5
10 2 3 15 5
3
and
3 1 5 15
The lowest common denominator is 15 Change each fraction to its equivalent fraction with a denominator of 15
3
10 So 2 1 3 3 5 15 15 13 2 1 3 5 15
Add the numerators but do not change the denominator.
55
Fractions
CHAPTER 4
Example 4 Work out 78 12 Give your answer as a mixed number.
Solution 4 7 8
12 78 48
The lowest common denominator is 8 Change 12 to the equivalent fraction with a denominator of 8
7 8
48 181
Add the numerators but do not change the denominator.
1 1 8 7 8
138
Change the improper fraction to a mixed number.
12 138
Fractions can be subtracted in a similar way.
Example 5 Work out 45 34
Solution 5 4 5
1260 and
3 4
4 5
34 1260 1250
4 5
34 210
1250
The lowest common denominator is 20 Change each fraction to its equivalent fraction with a denominator of 20 Subtract the numerators but do not change the denominator.
Exercise 4B In questions 1–5 give each answer as a mixed number or a fraction in its simplest form.
56
1 Work out a 13 12 e 23 14
b f
1 3 1 2
14 25
c g
1 5 1 5
14 23
d h
1 1 8 4 1 4 5 20
2 Work out a 25 38 e 45 170
b f
3 4 5 6
25 38
c g
2 1 3 6 9 3 4 10
d h
2 3 7 5 7 5 8 20
3 Work out a 12 14 e 34 12
b f
1 3 2 3
14 14
c g
1 3 1 2
19 25
d h
1 1 5 20 1 1 1 12 6
4 Work out a 34 23 e 56 35
b f
9 3 5 10 3 2 4 7
c g
7 2 8 5 1 7 3 20 4
d h
8 9 5 6
5 Work out a 37 25 e 78 23
b f
4 1 9 5 7 3 4 12
c g
5 6 4 5
d h
3 1 4 10 4 2 1 9 3 6
56
23 12 170
23 79
4.3 Addition and subtraction of mixed numbers
CHAPTER 4
4.3 Addition and subtraction of mixed numbers When adding mixed numbers, add the whole numbers and the fractions separately.
Example 6 Work out 213 412
Solution 6 24 6 1 3
Add the whole numbers.
12 26 36 56
Add the fractions.
213 412 6 56 656
Add the two results.
Sometimes adding the fractions gives an improper fraction. For example, adding the fraction parts of 223 and 412 gives 23 12 46 36 76 7 is an improper fraction. As a mixed number, 7 11 6 6 6 2 1 1 1 So 23 42 6 16 76 Mixed numbers can be subtracted in a similar way.
Example 7 Work out 323 112
Solution 7 31 2 2 3
Subtract the whole numbers.
12 46 36 16
Subtract the fractions.
2 16 216
Add the two results.
323 112 216
Example 8 Work out 414 2170
Solution 8 Method 1 414 147 and 2170 2170
Change mixed numbers to improper fractions.
5
85 17 4 20
2
and
5 1 7 4
2170 8250 5240 3210 3 1 20
11210
54 27 10 20
The lowest common denominator is 20 Change each fraction to its equivalent fraction with a denominator of 20
2
Subtract the numerators but do not change the denominator. Give the answer as a mixed number.
414 2170 11210 57
Fractions
CHAPTER 4
Method 2 42 2 1 4
Subtract the whole numbers.
170 250 1240 290
Subtract the fractions.
2 290 1 1 290 1 2200 290 1 1210 11210
Add the two results.
414 2170 11210
Exercise 4C 1 Work out a 245 135 e 235 134
b 359 89 f 123 112
c 634 112 g 434 123
d 445 12 h 323 149
2 Work out a 212 114
b 378 112
c 323 112
d 445 123
3 Work out a 1 13
b 3 25
c 6 514
d 8 423
4 Work out a 214 112 e 513 134
b 314 123 f 635 223
c 412 234 g 427 135
d 316 112 h 719 323
5 Work out a 315 2145 e 1258 323
b 838 334 f 356 325
c 623 89 g 8170 313
d 156 427 h 916 179
4.4 Multiplication of fractions and mixed numbers Multiplication by an integer is the same as repeated addition. So 2 49 is the same as 49 49 89 To multiply a fraction by an integer, multiply the numerator of the fraction by the integer. Do not change the denominator of the fraction.
Example 9 Work out 6 23
Solution 9 6 23 132 1 2 3
4
6 23 4
Multiply the numerator of the fraction by the integer. Do not change the denominator. Simplify the fraction. The answer is an integer in this case.
To multiply 34 by 23 3 4
23 162 12
Multiply the numerators 3 2 6 Multiply the denominators 4 3 12 Simplify the fraction. 1 6 ( ) of the area of the square is shaded. 2 12 To multiply two fractions, multiply the numerators and then multiply the denominators.
58
3 4
2 3
4.4 Multiplication of fractions and mixed numbers
CHAPTER 4
Example 10 Work out 23 25
Solution 10 2 2 4 3 5 15
Multiply the numerators 2 2 4 Multiply the denominators 3 5 15 4 is in its simplest form. 15
When multiplying fractions, it is sometimes possible to simplify the multiplication by cancelling.
Example 11 5 7 Work out 14 10
Solution 11 5 7 57 14 10 14 10 1
7 5 17 14 10 14 2
Cancel the 5 and the 10
2
1
7 11 1 14 2 2 2
Cancel the 7 and the 14
2
11 1 22 4 1 5 7 14 10 4 When multiplying mixed numbers, first write the mixed numbers as improper fractions.
Example 12 Work out 223 145
Solution 12 223 145 83 95
Change each mixed number into an improper fraction.
3
8 9 35
Cancel the 9 and the 3
24 445 5
Change the improper fraction into a mixed number.
1
Exercise 4D Give each answer in its simplest form.
1 Work out a 2 13 e 38 2
b 3 14 f 152 4
c 2 25 g 290 8
d 3 27 h 35 25 59
Fractions
CHAPTER 4
2 Work out a 35 12 e 23 27
b f
1 4 3 4
35 35
c g
1 2 3 5 7 3 5 10
d h
1 2 3 4
3 Work out a 34 25 e 134 89
b f
2 3 3 8 1 6 9 21 40
c g
1 0 11 9 28
d h
5 4 6 15 2 5 2 7 36 40
4 Work out a 114 13 e 113 214
b 135 12 f 312 114
c 223 15 g 313 145
d 37 312 h 217 245
5 Work out a 113 114 e 227 438
b 212 135 f 416 445
c 334 1110 g 637 159
d 123 415 h 813 2170
6 Work out a 34 56 136
b
c (123 56) 89
d (279 113) 412
1 7 20
45 38
35 1145
4.5 Division of fractions and mixed numbers 3 4
of this rectangle is shaded red.
Divide the red area by 2 Now 38 of the rectangle is shaded. So 34 2 38 also
3 4
12 38
So dividing by 2 is the same as multiplying by 12 1 is the reciprocal of 2 2 To work out 3 34 consider how many times 34 goes into 3
There are 142 in 3 whole squares, this is 4 lots of 34
So 3 34 4
also
3 43 4
So dividing by 34 is the same as multiplying by 43 4 3 3 is the reciprocal of 4 Similarly, the reciprocal of 3 (or 31) is 13 and the reciprocal of 27 is 72 To divide by a fraction ● change the division sign into a multiplication sign ● write down the reciprocal of the second fraction. 60
15 57
4.5 Division of fractions and mixed numbers
Example 13
Example 14
Work out 45 3
Solution 13 4 3 4 1 5 5 3 4 5
3
CHAPTER 4
Work out 56 34 Give your fraction in its simplest form. The reciprocal of 3 is 13 Multiply 45 by 13
4 15
Solution 14 2 5 3 5 4 6 4 6 3
The reciprocal of 34 is 43 So multiply 56 by 43
3
10 9 5 3 119 6 4
Write the improper fraction as a mixed number.
When dividing mixed numbers, first write the mixed numbers as improper fractions.
Example 15 Work out 245 2110
Solution 15 245 2110 154 2110 2
2
1
3
14 10 5 21
Write the mixed numbers as improper fractions. The reciprocal of 2110 is 1201
4 3 245 2110 113
Write the improper fraction as a mixed number.
Exercise 4E Give each answer in its simplest form. 1 Work out a 56 2 e 14 13
b f
3 8 3 5
2 12
c g
5 6 4 9
3 13
d h
5 8 5 6
2 Work out a 23 35 e 58 1352
b f
3 4 7 5 4 7 1 25 10
c g
4 3 5 10 2 0 8 21 15
d h
9 16 2 5 32
3 Work out a 312 7 e 112 34
b 245 110 f 249 23
c 213 19 g 715 190
d 334 5 h 513 49
4 Work out a 213 245 e 4190 245
b 314 149 f 556 119
c 334 145 g 712 114
d 623 289 h 2112 119
5 Work out a (12 152) 34
b 3 34 190
c 318 (212 138)
d 335 114 225
10 14 38 1156
61
Fractions
CHAPTER 4
4.6 Fractions of quantities A unit fraction has a numerator of 1 and the denominator is a non-zero positive integer. Examples of unit fractions are 12 14 15 and 110 To find a unit fraction of an amount, think of that amount divided into equal parts.
Example 16 Find 14 of £24
Solution 16 24 4 6 1 4
Finding 14 of an amount is the same as dividing the amount into 4 equal parts.
of £24 £6
To find a fraction of an amount where the numerator is more than 1, think of the calculation in two stages. Firstly, divide the amount by the denominator. Then multiply the result by the numerator.
Example 17 Find 23 of £24
Solution 17 24 3 8 8 2 16 2 3
Divide 24 by 3 The result is 8 Multiply 8 by 2
of £24 £16
Another way to find a fraction of a quantity is to multiply the quantity by the fraction. For example 8 2 24 16 3 1
In mathematics, the word ‘of’ means the same as ‘’
Example 18 Find 37 of 10
Solution 18 3 of 10 3 10 7 7
‘of’ means the same as ‘’
370 3 7
62
of 10 427
Change the improper fraction into a mixed number.
Exercise 4F 1 Find a 14 of 12 e 110 of 70
b f
1 3 1 8
of 18 of 32
c g
1 of 35 5 1 of 48 12
d h
1 of 24 6 1 of 100 20
2 Find a 23 of 15 e 56 of 24
b f
3 4 4 9
of 12 of 27
c g
2 of 20 5 7 of 50 10
d h
3 7 7 8
of 14 of 48
4.7 Fraction problems
CHAPTER 4
3 Find a 25 of £150 e 56 of 240 m
b f
3 of 120 grams 4 7 of 120 cm 10
c g
2 3 3 7
4 Find a 23 of 5 e 78 of 12
b f
2 5 3 7
of 4 of 8
c g
5 Find a 13 of 25
b
8 9
of 37
6 Find a 34 of £184 e 1156 of 336 m
b f
7 Find a 25 of £4 e 1372 of 20 kg
b f
d h
4 5 2 9
2 of 6 9 9 of 8 10
d h
5 of 16 12 5 of 24 9
c
6 7
d
5 8
5 of £496 8 3 9 50 of £1750
c g
5 of £318 6 7 of 660 kg 40
d h
1 7 20 of £460 2 9 100 of 40 km
3 of 12 m 8 9 of 175 grams 10
c g
7 16 3 40
d h
5 of 78 cm 12 3 of £68.40 4
of 48 cm of 280 kg
of 1145
of 6 km of £1420
of £230 of 6120 km
of 2245
4.7 Fraction problems Problems can involve fractions.
Example 19 In a cinema 2 of the audience are women. 5 1 of the audience are men. 8 All the rest of the audience are children. What fraction of the audience are children?
Solution 19 2 6 2 1 1 1 5 5 8 40 40 40
Add 25 and 18 to find the fraction of the audience who are women or men.
1 2410 4400 2410 1490
Subtract 2410 from 1 to find the fraction of the audience who are children.
1 9 40
of the audience are children.
Example 20 A school has 1800 pupils. 860 of these pupils are girls. 3 of the girls like swimming. 4 2 of the boys like swimming. 5 Work out the total number of pupils in the school who like swimming.
Solution 20 3 860 645 4
Work out the number of girls who like swimming.
1800 860 940
Work out the number of boys in the school.
2 5
940 376
Work out the number of boys who like swimming.
Work out the total number of pupils who like swimming. 645 376 1021 1021 pupils like swimming.
63
Fractions
CHAPTER 4
Exercise 4G 1 Simon spends 12 of his money on rent and 13 of his money on transport. a What fraction of his money does he spend on rent and transport altogether? b What fraction of his money is left? 2 Dawn drives for 34 of a journey. The journey lasts for 148 minutes. For how many minutes does Dawn drive? 3 There are 800 students in a school. 35 of the students are boys. Work out the number of boys in the school. 4 Last season, Pearson Athletic won 170 of its matches, drew 15 and lost the rest. What fraction of its matches did it lose? 5
1 2
of a garden is lawn. 25 of the garden is a vegetable patch. The rest of the garden is a flower bed. What fraction of the garden is a flower bed?
6
8 9
of an iceberg lies below the surface of the water. The total volume of an iceberg is 990 m3. What volume of this iceberg is below the surface?
7 There are 36 students in a class. Javed says that 38 of these students are boys. Explain why Javed cannot be right. 8 John walks 212 miles to the next village. He then walks a further 223 miles to the river. How far has he walked altogether? 9 Tammy watches 2 films. The first film is 134 hours long and the second one is 213 hours long. Work out the total length of the two films. 10 Two sticks are 212 metres and 113 metres long. Work out the difference between the lengths of the two sticks. 11
2 3
of a square is shaded. 34 of the shaded part is shaded blue. What fraction of the whole square is shaded blue?
12 In a crowd, 25 of the people are female. 170 of the females are girls. What fraction of the crowd is girls? 13 DVDs are sold for £14 each. 25 of the £14 goes to the DVD company. How much of the £14 goes to the DVD company? 14 A school buys some textbooks. The total price of the textbooks is £2400 The school gets a discount of 18 off the price of the textbooks. Work out how much the school pays for the textbooks. 15 Alison, Becky and Carol take part in a charity relay race. The race is over a total distance of 258 kilometres. Each girl runs an equal distance. Work out how far each girl runs. 64
Chapter 4 review questions
CHAPTER 4
Chapter summary You should now know:
that equivalent fractions are fractions that are equal
how to find an equivalent fraction by multiplying both the numerator and denominator by the same number
how to cancel a fraction to obtain its simplest form
how to order fractions by writing each fraction with the same denominator
that an improper fraction is one in which the numerator is greater than the denominator
that a mixed number consists of a whole number and a fraction
how to convert between mixed numbers and improper fractions
that to add (or subtract) fractions with the same denominator, add (or subtract) the numerators but do not change the denominator
that to add or subtract fractions with different denominators, firstly find the lowest common denominator and then change each fraction to its equivalent fraction with this denominator
how to add (or subtract) mixed numbers by adding (or subtracting) the whole numbers and the fractions separately
how to multiply fractions by multiplying the numerators and then multiplying the denominators
how to multiply or divide mixed numbers by firstly writing the mixed numbers as improper fractions
how to divide by a fraction by ● changing the division sign into a multiplication sign ● writing down the reciprocal of the second fraction
how to find a fraction of an amount by dividing the amount by the denominator and then multiplying the result by the numerator.
Chapter 4 review questions
1 Work out a 14 of £48
b
1 5
of £50
c
1 3
of £60
d
1 10
2 Work out a 34 of £44
b
2 3
of £18
c
2 5
of £35
d
c
1 3
14
d
of £40
e
1 6
of £30
3 5
of £100
e
4 5
of £45
1 4
35
e
4 5
23
3 Change to improper fractions b 845 a 223 4 Work out a 12 13
b
2 3
14
5 Simon spent 13 of his pocket money on a computer game. He spent 14 of his pocket money on a ticket for a football match. Work out the fraction of his pocket money that he had left.
(1387 June 2003)
65
Fractions
CHAPTER 4
6 Asif, Curtly and Barbara share some money. Asif receives 38 of the money. Barbara receives 13 of the money. What fraction of the money does Curtly receive?
(1388 March 2004)
7 Work out 1 (12 16)
(1387 November 2004)
8 Work out, giving your answers as mixed numbers b 434 245 a 345 223 9 Work out and simplify where possible b 152 2 c a 17 4
1 8
4
d
3 10
e
3 8
2
c
6 7
3
d
8 9
3
e
4 9
5
11 Work out and simplify where possible b 13 45 c a 45 14
1 4
34
d
1 5
1201
e
6 11
12 Work out and simplify where possible b 14 of 35 c a 13 of 35
1 2
of 67
d
1 4
of 181
e
1 5
of 1103
13 Work out, giving each answer in its simplest form b 56 25 c 170 56 a 38 25
d
5 6
190
e
5 9
265
14 Work out, giving each answer in its simplest form b 57 1101 c 29 320 a 34 15
d
1 8 35
e
2 1 40
10 Work out a 25 2
15 Work out a 16 49
b
4 7
3 7
2
2
67
13
38
8
(1388 March 2002)
16 Work out 23 56 Give your fraction in its simplest form.
(1388 January 2004)
b
17 Work out, giving your answers as mixed numbers b 423 125 a 123 2130 18 a Work out the value of 23 34 Give your answer as a fraction in its simplest form. b Work out the value of 123 + 234 Give your answer as a fraction in its simplest form. 19 A school has 1200 pupils. 575 of these pupils are girls. 2 of the girls like sport. 5 3 of the boys like sport. 5 Work out the total number of pupils in the school who like sport. 20 Work out 334 223 21 Work out 312 123 Give your answer as a mixed number in its simplest form. 66
(1387 June 2005)
(1387 November 2003) (1388 March 2003)