If 5/x = 15/(x + 20) what is x/5?

Question

Find the value of x/5 based on the above proportion, using a quick method to save time.

Answer 1

5 / x = 15 / (x + 20)

15 x = 5 * (x + 20) [cross-multiply]

15x = 5x + 100 [apply distributive property on right side]

10x = 100 [subtract 5x from both sides]

x = 10 [divide both sides by 10]

x / 5 = 2 [divide both sides by 5]

Answer 2

Since x/5 is the reciprocal of 5/x, we know that we can flip the fraction on the right hand side will be flipped.

Thus, x/5 = (x + 20)/15

Now we cross multiply, 15x = 5(x + 20)

Simplify: 15x = 5x + 100

Subtract 5x from each side: 10x = 100

Divide 10: x = 10

Now plug 10 back into the right hand side: (10 + 20)/15

So, the answer is 2.