Who is good at math? HELPPP!!!

Sarie_Bronish

My friend weighs 187 pounds and is 38% body fat currently.

I know that 38% of 187 pounds = 71 pounds.
This would leave 116 pounds as LBM

She wants to know what she would weigh at 33% body fat. - but I apparently skipped class those days in math class because I cant figure this out after 3 sheets of paper, 100+ equations, and more answers than I care to admit. Help me please!!!

Sarie_Bronish

cool points if you show your work :P

j6o4

She wants to lose 5%, 38% - 33% = 5%
187lbs x 0.05 = 9.35lb, this is how much she needs to lose.
187lbs - 9.35lbs = 177.65lbs, this is how much she would be at 33% if she loses no muscle in the process.

Aaron_K123

If her lean mass is 116 pounds and she is at 33% bodyfat and you want to determine her weight X then:

116 + 0.33 * X = X


Solve for X. 57 pounds of fat, 173 pounds would be her bodyweight assuming no loss of lean mass.

EvanKeel

are you assuming she only lost fat? If so, it should be fairly easy to figure out a 5% reduction in weight..unless I'm missing something.

Aaron_K123

She wants to lose 5%, 38% - 33% = 5%
187lbs x 0.05 = 9.35lb, this is how much she needs to lose.
187lbs - 9.35lbs = 177.65lbs, this is how much she would be at 33% if she loses no muscle in the process.

But if she is 177.65 pounds at 33% bodyfat her lean mass would be 177.65 - (.33 * 177.6) = 119 which would mean she would have put on 3 pounds of lean mass.

Answer is 173

EvanKeel

She wants to lose 5%, 38% - 33% = 5%
187lbs x 0.05 = 9.35lb, this is how much she needs to lose.
187lbs - 9.35lbs = 177.65lbs, this is how much she would be at 33% if she loses no muscle in the process.

But if she is 177.65 pounds at 33% bodyfat her lean mass would be 177.65 - (.33 * 177.6) = 119 which would mean she would have put on 3 pounds of lean mass.

Fair

EDIT: I guess alternatively one could say X= (116/0.67) if assume 116 is constant.

j6o4

She wants to lose 5%, 38% - 33% = 5%
187lbs x 0.05 = 9.35lb, this is how much she needs to lose.
187lbs - 9.35lbs = 177.65lbs, this is how much she would be at 33% if she loses no muscle in the process.

But if she is 177.65 pounds at 33% bodyfat her lean mass would be 177.65 - (.33 * 177.6) = 119 which would mean she would have put on 3 pounds of lean mass.

Answer is 173

hmm, guess i made a mistake.

brisingr86

If her lean mass is 116 pounds and she is at 33% bodyfat and you want to determine her weight X then:

116 + 0.33 * X = X


Solve for X. 57 pounds of fat, 173 pounds would be her bodyweight assuming no loss of lean mass.

I did the math differently, but came up with the same answer.
1. Assuming LBM should remain constant: lean body mass=weight * (1-%BF).
2. 187*(1-0.38)=X* (1-0.33)-->solve for X
3. 187*0.62=0.67X
4. 115.94/0.67=X
5. 173.04=X=weight at 33% body fat

yewbic

x - 116 = x(.33)
x - .33x = 116
.67x = 116
x = 173

Sarie_Bronish

thank you - yes, I WAYYYYYYYYYYYYYYYYYYYY over thought this, and i shouldve stuck to my gut. I got all twisted up and *kitten* deep in numbers that didnt matter while trying to be accurate.

Aaron_K123

EDIT: I guess alternatively one could say X= (116/0.67) if assume 116 is constant.

Yeah that would be the easy way really then you don't even have to solve for X in the formula I layed out. Of course if you do do the algebra you end up with X = (116/.67) as laid out in what yewbic did. Guess I never showed my work ;-)