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Question
The variable x varies directly as y and x = 80 when y is 160. What is y when x is 64?
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Solution
If x varies directly as y.
∴ `x/y = k` (constant) ...(i)
If x = 80 and y = 160
∴ `x/y = 80/160 = 1/2`
⇒ `k = 1/2`
When x = 64, then from equation (i),
`64/y = 1/2` ...[Putting the value of k]
⇒ y = 64 × 2 = 128
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