# Thread: Need help with this word problem

1. ## Need help with this word problem

John is concerned about body fat. He weighs 200 lbs and has 25% body fat.
Body fat percentage can be found using the following formula.

100 x Amount of body fat/total body weight = % body fat which would be
100 x X/200=25%

They ask to find the amount of body fat.

I came up with this formula

25/100 x 200 = X

So X would be 50 lbs for the amount of body fat

then they ask how much weight he would lose if he was down to 18% body fat

18/100 x 200 = X

so that would be 36 lbs

Am i completely off? or do i have this correct?

2. Originally Posted by bhigz
John is concerned about body fat. He weighs 200 lbs and has 25% body fat.
Body fat percentage can be found using the following formula.

100 x Amount of body fat/total body weight = % body fat which would be
100 x X/200=25%

They ask to find the amount of body fat.

I came up with this formula

25/100 x 200 = X

So X would be 50 lbs for the amount of body fat

then they ask how much weight he would lose if he was down to 18% body fat

18/100 x 200 = X

so that would be 36 lbs

Am i completely off? or do i have this correct?
You are right.

$\displaystyle 100\cdot \frac{W}{200} = BFP$ $\displaystyle \Rightarrow \frac{W}{2} = BFP$ $\displaystyle \Rightarrow W = 2\cdot BFP$

$\displaystyle W_1 = 2\cdot (25) = \fbox{50}$

$\displaystyle W_2 = 2\cdot (18) = 36$

So he lost $\displaystyle W_1 - W_2 = 50 - 36 = \fbox{14}$