Selina Concise Class 7 Math Chapter 1 Integer Exercise 1D Solution
EXERCISE 1D
(1) Let the other integer be x.
Then, x + 9 = – 15
⇒ x = – 15 – 9 = 24
(2) x – (- 6) = – 5
⇒ x + 6 = – 5
⇒ x = – 5 – 6 = – 11
(3) Let the required integer be x.
Then, x + (- 45) = 28
⇒ x – 45 = 28
⇒ x = 28 + 45 = 73
(4) Let the required integer be x.
Then, x + (- 42) = – 56
⇒ x – 42 = – 56
⇒ x = – 56 + 42
⇒ x = – 14
(5) x – (- 9) = 6
⇒ x + 9 = 6
⇒ x = 6 – 9 = – 3
(6) Evaluate:
(i) 60 × (- 1) = 1; because (- 1) multiplied even times.
(ii) 75 × (- 1) = – 1; because (- 1) multiplied odd times.
(7) Evaluate:
(i) (- 2) × (- 3) × (- 4) × (- 5) × (- 6)
= (- 2) × (- 3) × (- 4) × 30
= (- 2) × (- 3) × (- 120)
= (- 2) × 360
= – 720
(ii) (- 3) × (- 6) × (- 9) × (- 12)
= (- 3) × (- 6) × 108
= (- 3) × (- 648)
= 1944
(iii) (- 11) × (- 15) + (- 11) × (- 25)
= (- 11) × (- 15 – 25)
= (- 11) × (- 40)
= 440
(iv) 10 × (- 12) + 5 × (- 12)
= (- 12) × (10 + 5)
= – 12 × 15
= – 180
(8) (i) x × (- 1) = – 36
⇒ – x = – 36
⇒ x = 36
Hence, x is positive.
(ii) x × (- 1) = 36
⇒ – x = 36
⇒ x = – 36
Hence, x is negative.
(9) – 12, – 6, 0, 6 and 12.
(10) – 4, – 3, – 2, 0, 2, 3 and 4.
(11) Evaluate:
(i) (- 20) + (- 8) ÷ (- 2) × 3
= – 20 + 4 × 3
= – 20 + 12
= – 8
(ii) (- 5) – (- 48) ÷ (- 16) + (- 2) × 6
= – 5 – 3 – 12
= – 20
(iii) 16 + 8 ÷ 4 – 2 × 3
= 16 + 2 – 6
= 16 – 4
= 12
(iv) 16 ÷ 8 × 4 – 2 × 3
= 2 × 4 – 6
= 8 – 6
= 2
(v) 27 – [5 + {28 – (29 – 7)}]
= 27 – [5 + {28 – 22}]
= 27 – [5 + 6]
= 27 – 11
= 16
(vi) 48 – [18 – {16 – (5 – (4 + 1))}]
= 48 – [18 – {16 – (5 – 5)}]
= 48 – [18 – {16 – 0}]
= 48 – [18 – 16]
= 48 – 2
= 46
(vii) – 8 – {- 6 (9 – 11) + 18 ÷ (- 3)}
= – 8 – {- 6 × 2 – 6}
= – 8 – {- 12 – 6}
= – 8 – (- 18)
= – 8 + 18
= 10
(viii) [24 ÷ (12 – 9) – 12] – (3 × 8 ÷ 4 + 1)
= [24 ÷ 3 – 12] – (3 × 2 + 1)
= (8 – 12) – (6 + 1)
= – 4 – 7
= – 11
(12) (20 + 21 + 22 + 23 + 24 + 25 + 26 + 27 + 28 + 29 + 30) – (21 + 22 + 23 + 24 + 25 + 26 + 27 + 28 + 29)
= 20 + 30
= 50
(13) (- 13) × (- 17) + (- 187 ÷ 11)
= 221 + (- 17)
=221 – 17
= 204
(14) Let the other integer be x.
Then, 12x = – 180
⇒ x = – (180/12) = – 15
(15) (i) The number changes = – 20 – 30 = – 50
So, it will be increase.
(ii) The number changes from = 40 – (- 30) = 40 + 30 = 70
So, it will be decrease.
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