Page 75 - Start Up Mathematics_7

–2 1 –2 5 –2 × 5 –10
(e) ÷ = × = =
13 5 13 1 13 × 1 13

2 –7 2 65 2 × 65 130 –130 –10
(f) ÷ = × = = = =
13 65 13 –7 13 × –7 –91 91 7
2 4
Example 16: The cost of 7 metres of cable wire is ` 128 . Find the cost of wire per metre?
3 5
2 4
Solution: Cost of 7 metres of wire = ` 128
3 5
23 644
i.e., cost of metres of wire = `
3 5
Cost of 1 metre of wire = 644 ÷ 23 = 644 × 3 = 1,932 = ` 16 4
5 3 5 23 115 5

EXERCISE 4.2

–3 –6 5 8 –8 3
1. Add: (a) and (b) and (c) and
17 51 21 35 17 51
–9 6 1 –9 13 11
2. Subtract: (a) from (b) 3 from (c) from
22 11 4 –4 48 36
3 6 –11 1
3. Write the additive inverse of: (a) (b) (c) (d) –7
13 –23 30 3
5 –27 –17 1
4. Write the reciprocal of: (a) (b) (c) (d) 2
4 13 39 7
2 3 1 –24 3 –7 1 5
5. Multiply: (a) × (b) × (c) × (d) 2 ×
3 –7 8 13 11 19 3 14
–2 1 1 7 –4 –5 7
6. Divide: (a) –6 ÷ (b) 2 ÷ 5 (c) ÷ (d) ÷
13 5 25 13 65 8 4

Maths Lab Activity (Worksheet)

Properties of Rational Numbers

Let’s verify the properties of rational numbers with respect to addition:
(i) Closure property of addition (ii) Commutative property of addition

1 3 5 1 1 7 1 1
 + = which is again rational  + = = +
2 4 4 3 4 12 4 3
∴ closure property holds. ∴ commutative property holds.
(iii) Associative property of addition (iv) Existence of additive identity

1 1 5 5 1 1 5 a a a
 + + = = + +  + 0 = = 0 + , for every
2 3 3 2 2 3 3 b b b
∴ associative property holds. rational number a
b
∴ identity element, i.e., 0 exists.

67