Question

Suppose p varies directly with d, and p = 3 when d = 5. What is the value of d when p = 12?

Answer 1

20

Answer 2

p varies directly with d
p = Kd

Answer 3

p = 5/3d which means that 20=5/3*12

Answer 4

That is the formula to for direct variation. Plug in the given to determine the constant K
then do the formula again with the K and the p = 12 to solve for d

Answer 5

K is equal to y/x in the for y=Kx

Answer 6

so if p=Kd, then K= d/p

Answer 7

therefore you can derive that 12=(p/d)d and because K can be any instance of p/d, 3/5 works, so you just see what time 3/5 equals 12, otherwise known as multiplying 12 by 5/3