Question

Suppose that y varies directly with x and y = 10 when x = 20. What is y when x = 15?

Answer 1

Answer: y = 7.5

Step-by-step explanation:

Suppose that y varies directly with x

That is, y∝x

Convert y∝x to a full equation by introducing a constant k to the right hand side.

Therefore, y = kx

Given that y = 10 and x = 20

Substitute y and x in the equation above. We have;

10 = k(20)

10 = 20k

20k = 10

k = 10/20

k = 0.5

Since k = 0.5, the equation y = kx becomes y = 0.5x

Now, to find y if x = 15, substitute x in equation y = 0.5x

Therefore, y = 0.5(15)

y = 7.5