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Example 3: Siya’s father filled 8 litres of petrol in his car and he used up 7 litres on a
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visit to the zoo with her. How much petrol is left in his car?
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Solution: Petrol filled in the car = 8 litres
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Petrol used on visiting the zoo = 7 litres
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2
2
Therefore, the petrol left in the car = 8 – 7 = 25 – 23 = 25 – 23 = litre.
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Thus, litre of petrol is left in the car.
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addition and subtraction of unlike Fractions
To add or subtract unlike fractions, first convert them into like fractions and then add or
subtract as like fractions.
Example 4: Solve the following.
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( a) + 7 3 ( b) – 8 5 ( c) 7 2 + 2 7 ( d) 7 – 3 5
9 8 9 6 15 12 9 4

Solution:
( a) Convert the given fractions into their respective equivalent fractions having the

same denominator equal to the LCM of the denominators of the given fractions.
Here, the LCM of 9 and 8 is 72.

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7
Therefore, + = 7 × 8 + 3 × 9
9 8 9 × 8 8 × 9

= 56 + 27 = 56 + 27 = 83 = 1 11
72 72 72 72 72

( b) Convert the given fractions into their respective equivalent fractions having the
same denominator equal to the LCM of the denominators of the given fractions.

Here, the LCM of 9 and 6 is 18.

8
5
Therefore, – = 8 × 2 – 5 × 3 = 16 – 15 = 16 – 15 = 1
9 6 9 × 2 6 × 3 18 18 18 18
( c) First convert the mixed fractions into improper fractions and then convert the unlike
fractions into their respective equivalent fractions having the same denominator
equal to the LCM of the denominators of the given fractions.
Here, the LCM of 15 and 12 is 60.

2 7 107 31 107 × 4 31 × 5
Therefore, 7 + 2 = + = +
15 12 15 12 15 × 4 12 × 5
428 155 428 + 155 583 43
= + = = = 9
60 60 60 60 60

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