f(x) = x/1+x. For which x is f(x) = 1/4

Question

I thought I had to substitute the 1/4 but, it didn't work out.

Answer 1

First of all, you need to group things in parentheses.

f(x) = x / (1 + x)

Set f(x) = 1/4, and solve for x.

1/4 = x / (1 + x)

1 + x = 4x

1 = 3x

x = 1/3

Test the answer.

(1/3) / (1 + 1/3) = 1 / (3 + 1) = 1/4 (good)