SAT Mathematics Practice Test 3

Multiplying each side of $\frac{5}{x} = \frac{15}{x+20}$ by $x(x+20)$ gives $15x = 5(x+20)$ Distributing the 5 over the values within the parentheses yields $15x = 5x + 100$ and then subtracting 5x from each side gives $10x = 100$ Finally, dividing both sides by 10 gives $x = 10$. Therefore, the value of $\frac{x}{5}$ is $\frac{10}{5} = 2$ Choice A is incorrect because it is the value of $x$,not $\frac{x}{5}$ Choices B and D are incorrect and may be the result of errors in arithmetic operations on the given equation.