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Question
x varies inversely as y, when x = 15 then y = 10, if x = 20 then y = ?
Solution
It is given that x varies inversely as y, i.e., `x α 1/y`
∴ \[x = \frac{k}{y}\] , where k is constant of variation
⇒ x × y = k
When x = 15, y = 10.
∴ k = 15 × 10 = 150
So, the equation of variation is xy = 150.
When x = 20,
20y = 150
⇒ y = \[\frac{150}{20}\]
y = 7.5
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