(贈送20點)..........maths

Question

The weights of copper and zinc in an alloy are in the ratio 8:5.

a)If the alloy contains 80g of copper, how much zinc does it contain?

b)If the alloy weights 39g, what are the weights of copper and zinc in it?

Answer 1

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a) the weight of zinc=80x5/8

=50g

b) the weight of copper=39x8/(8+5)

=39x8/13

=24g

the weight of zinc=39x5/(8+5)

=39x5/13

=15g

Answer 2

Let weight of copper = C, weight of Zine = Z

i.e. C / Z = 8 / 5, C = (8/5)Z

a)

if C = 80g, then 80 = (8/5)Z

Z = (80 x 5) / 8 = 50g

b)

C + Z = 39 ..... (1)

C = (8/5)Z ...... (2)

put (2) into (1),

(8/5)Z + Z = 39

(13/5) Z = 39

Z = (39 x 5) / 13

Z = 15 ..... (3)

put (3) into (1)

C = (8/5) x 15

C = 24

so, C = 24g and Z = 15g