If x varies directly with y and x = 2.5 when y = 10, find x when y = 16.
1.5, 8, 7.5, 4

Solution:

x varies directly with y

x ∝ y (x directly proportional to y)

x = k.y where k is a constant of proportionality

Now substitute the value of x and y

x = k.y

2.5 = k (10)

k = 0.25

Determine the value of x by substituting the value of k and y

x = k . y

x = (0.25) (16)

So we get

x = 4

Therefore, the value of x is 4.

If x varies directly with y and x = 2.5 when y = 10, find x when y = 16. 
1.5, 8, 7.5, 4

Summary:

If x varies directly with y and x = 2.5 when y = 10, x is 4 when y = 16.