Question

An alloy contains only zinc and aluminium in the ratio 7:9.If the weight of the alloy is 8kg then find the weight of aluminium?

Answer 1

z = weight of zinc

a = weight of aluminium

z / a = 7 / 9

Multiply both sides by a

z = 7 a / 9

z + a = 8

7 a / 9 + a = 8

7 a / 9 + 9 a / 9 = 8

16 a / 9 = 8

Multiply both sides by 9

16 a = 72

a = 72 / 16 = 8 ∙ 9 / 8 ∙ 2 = 9 / 2 = 4.5 kg

weight of aluminium = 4.5 kg

Proof:

z = 7 a / 9 = 7 ∙ 4.5 / 2 ∙ 4.5 = 7 / 2 = 3.5 kg

weight of zinc = 3.5 kg

z / a = ( 7 / 2 ) / ( 9 / 2 ) = 7 / 9