
Algebra PreAlgebra and Basic Algebra Math Forum 
 LinkBack  Thread Tools  Display Modes 
September 8th, 2015, 10:03 AM  #1 
Newbie Joined: Sep 2015 From: USA Posts: 2 Thanks: 0  Find The Density of the body to find fat precentage
From one of my assignments. If someone could work this out and explain step by step, I would gratefully appreciate it.  Another use of density is determining the percentage of fat in a human body. With a wellengineered weighing system, body density can be determined with great accuracy by completely submerging a person in water and calculating the volume of the displaced water from the weight of the displaced water. Fat cells in humans are composed almost entirely of pure triglycerides with an average density of about 0.9 kg/L. (kg/L are equivalent to g/mL, but easier to use with larger objects like the human body.) Most modern body composition laboratories today use the value of 1.1 kg/L for the density of the “fat free mass”, a theoretical tissue composed of 72% water (density = 0.993), 21% protein (density = 1.340) and 7% mineral (density = 3.000) by weight. A correction is made for the buoyancy of air in the lungs and other gases in the body spaces. To find the percentage of fat we can assume that, if we set x to the fat percentage, 100 – x is the rest of the “fat free mass” of the body. The calculation is: Density of the body = (0.9)x + (1.1)(1x) Rearranging the equation to solve for x allows the calculation of the fraction of the body that is fat. Multiplying by 100 gives the percent fat. A 35 yearold female has a mass of 78 kg. When placed in a tank containing 1000 L of water, the volume in the tank increases to 1075 L. Last edited by skipjack; September 8th, 2015 at 03:59 PM. 
September 8th, 2015, 01:12 PM  #2  
Math Team Joined: Jul 2011 From: Texas Posts: 2,883 Thanks: 1503 
body density = $\displaystyle \frac{78 \, kg}{75 \, L} = 1.04 \, kg/L$ Quote:
1.1x  0.9x = 1.1  1.04 0.2x = 0.06 x = 0.3 30% body fat ... sounds reasonable to me  
September 8th, 2015, 08:11 PM  #3 
Newbie Joined: Sep 2015 From: USA Posts: 2 Thanks: 0 
Thanks Skeeter. I was reading too much into the problem and kept getting lost. Thanks for the help.


Tags 
body, density, fat, find, precentage 
Search tags for this page 
Click on a term to search for related topics.

Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Find a probability density function  Lena  Probability and Statistics  3  March 14th, 2015 02:10 PM 
Deriving Conditional Density from Joint Density  Relmiw  Advanced Statistics  1  July 7th, 2013 03:05 AM 
Find Sk and Find Kv ( i got example formula below)  kingkos  Algebra  5  November 24th, 2012 11:40 PM 
I want to find the distance in algebra find it  kevinman  Algebra  8  March 8th, 2012 05:53 AM 
help on to find probability density function!!!  musademirtas  Advanced Statistics  2  July 2nd, 2011 08:55 PM 