Question

When x varies directly as 2y and x=6 when y=20 find y when x=9
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Answer 1

x=k×2y

substitute x for 6 and y for 20

6=2(20)×k

6=40k

Divide both sides by the coefficient of k

6/40=40k/40

3/20=k

To find y, when x=9

9=3/20×2y

9=6y/20

cross multiply

9×20=6y×1

180=6y

Divide both sides by the coefficient

y=30