Problem Solving

If 5n/(4n - x) = (0.788)^(-1) , then x/n =

A) 3/500
B) 3/250
C) 3/125
D) 3/50
E) 3/25
Source: www.gmatprepnow.com

Answer: D
Difficulty level: 650 - 700

Hi Brent@GMATPrepNow,
Let's take a look at your question.

$$\frac{5n}{\left(4n-x\right)}=\left(0.788\right)^{-1}$$
$$\frac{5n}{\left(4n-x\right)}=\frac{1}{0.788}$$
$$\frac{5n}{\left(4n-x\right)}=\frac{1000}{788}$$
$$\frac{5n}{\left(4n-x\right)}=\frac{250}{197}$$
$$197\left(5n\right)=250\left(4n-x\right)$$
$$197\left(n\right)=50\left(4n-x\right)$$
$$197n=200n-50x$$
$$50x=200n-197n$$
$$50x=3n$$
$$\frac{x}{n}=\frac{3}{50}$$

Therefore, Option D is correct.

Hope it helps.
I am available if you'd like any follow up.