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?

Answer 1

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.