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

**Direct proportion is** the relationship between two variables whose ratio is equal to a constant value.

## Answer: If x and y vary directly, and x = 12 when y = 3, then the value of x when y = 9, is equal to 36.

Let's look into the relationship between x and y.

**Explanation:**

Given: x = 12, y = 3

Since, x is directly proportional to y we have,

x ∝ y

=> x = ky (where, k = constant of proportionality)

=> x/y = k ----------------------- (1)

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

k = 12/3 = 4

Thus, x/y = 4 (from equation (1))

Now, y = 9, x = ?

x = ky

=> x = 4 × 9 (since, k = 4)

=> x = 36

### Thus, if x and y vary directly, and x = 12 when y = 3, then the value of x when y = 9, is equal to 36

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