When 2 quantities are in direct proportion, as one increases so does the other or if one decreases so does the other

The general formula for this is: y = kx

**For example:**

If y is directly proportional to x when x = 12 then y = 3. Find the constant of proportionality and the value of x when y = 8.

We know that y is proportional to x so y = kx

To find the value of k substitute the values y = 3 and x = 12 into y = kx

3 = k × 12

So k = 3/12 = 1/4

To find the value of x , when y = 8 substitute y = 8 and k = 1/4 into y = kx

8 = (1/4) x

**So x = 32 when y = 8**

## Comments

No comments have yet been made