Question

If x varies directly with y and x = 3.5 when y = 14, find x when y = 18.

Answer 1

y = kx

x = 3.5 when y = 14
so

14 = 3.5k
k = 14/3.5
k = 4
when y = 18.
y = kx
18 = 4x
x = 18/4
x = 4.5

answer

when y = 18, x = 4.5

Answer 2

the value of x= 4.5

Explanation:

If x varies directly with y and x = 3.5 when y = 14

x varies directly with y , so equation is x= ky

where k is the constant of proportionality

x = 3.5 when y = 14, use the given values and find out k

Plug in the given values in x=k y

3.5= k * 14

Divide by 14 on both sides

0.25= k

So the value of k = 0.25

Now find out x when y= 18

x= ky

x= 0.25 * 18= 4.5