Page 22 - ICSE Math 7

(b) 2[11 –{22 – (119 – 55 ÷ 5 + 5 of 3)}]
= 2[11 –{22 – (119 – 11 + 15)}] (Removing vinculum and changing ‘of’ to
multiplication)
= 2[11 –{22 – (123)}]
= 2[11 –{22 – 123}] (Removing small brackets)

= 2[11 –{–101}] = 2[11 + 101] (Removing curly brackets)
= 2[112] = 224

EXERCISE 1.2

1. What must be added to –25 to get 9?
2. What must be subtracted from 121 to get –222?
3. Evaluate the following.
(a) (+215) + 560 (b) (–415) – (–99) + 65 (c) –(–71) – (–100) + 200

(d) (+65) + 71 –25 – (–31) (e) 35 + (–25) – 15 – (+22)
4. If the product of two integers is –1,008 and one of the integers is –24, find the other integer.
5. Find the following products.
(a) 11 × (–21) × 7 (b) 22 × (–5) × (–11) × (–3)
(c) 15 × 2 × (–9) × (–6) (d) (–10) × (–3) × (–19) × (–2)
6. Find the quotient.
(a) 156 ÷ 13 (b) (–182) ÷ 14 (c) 0 ÷ (–10)

(d) 21 ÷ (–21) (e) (–175) ÷ (–1) (f) (–221) ÷ (–17)
7. Simplify the following.
(a) 24 – {12 – (121 ÷ 11 × 3) + 5} (b) 4 of {(12 × 5 + 3 – 4) ÷ 4}
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(c) 5 – [8 – {16 + (21 × 3 – 6 – 3)}] (d) 3a – 2b + 15a ÷ 5a + 4c – 2a
(e) 8 – [8 – {8 – (8 – 8 – 8)}]

Word Problems

Example 11: A certain freezing process requires the room temperature to be lowered from 30°C at
the rate of 5°C every hour. What will be the room temperature 8 hours after the process
begins?

Solution: Temperature to be lowered by 5°C every hour.
∴ Temperature to be lowered in 8 hours = 8 × 5°C = 40°C
Room temperature in the beginning = 30°C
∴ Room temperature after 8 hours = 30°C – 40°C = –10°C

Example 12: In a class test containing 20 questions, 4 marks are awarded for every correct answer,
1 mark is deducted for every incorrect answer and 0 is given for questions not attempted.
Answer the following questions.

(a) Rohit gets four correct and six incorrect answers. What is his score?
(b) Arushi gets five correct and five incorrect answers. What is her score?
Solution: (a) Rohit’s score = 4 × 4 + 6 × (–1) = 16 – 6 = 10

(b) Arushi’s score = 5 × 4 + 5 × (–1) = 20 – 5 = 15

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