If x and y vary directly, and x = 12 when y = 3, what will be the value of x when y = 9?

Solution:

Given: x = 12, y = 3

Since, x is directly proportional to y we have,

x ∝ y

⇒ y = kx ------> (1)

where k = constant of proportionality

⇒3 = k × 12

Substitute the values of x and y in equation(1) we get,

k = 3/12 = 1/4

Now let's find the value of x when y = 9

Again substitute the values in equation (1)

y = kx

9 = 1/4 × x

x = 36

Thus x = 36 and when y = 9

If x and y vary directly, and x = 12 when y = 3, what will be the value of x when y = 9?

Summary:

The value of x when y = 9 is 36.