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Question
Let y varies directly as x. If y = 12 when x = 4, then write a linear equation. What is the value of y when x = 5?
Solution
Given that, y varies directly as x.
i.e., y ∞ x ⇒ y = kx [where, k = arbitrary constant] ...(i)
Given, y = 12 and x = 4
12 = 4k
⇒ `k = 12/4` ...[From equation (i)]
∴ k = 3
On putting the value of k in equation (i), we get
y = 3x ...(ii)
When x = 5, then from equation (ii), we get
y = 3 × 5 ⇒ y = 15
Hence, the value of y is 15.
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