Question

Part ASome athletes have as little as 3.0 % body fat. If such a person has a body mass of 77 kg, how many pounds of body fat does that person have?Express your answer using two significant figures.

Answer 1

First, we have to remember what a mass percentage (in a body) is:

`\%\text{ m/m = }\frac{mass\text{ of substance}}{mass\text{ of the body}}*100`

We have the percentage and the body's mass. It means that we can calculate the amount of fat that these people have:

`\begin{gathered} 3.0\text{ }\%\text{ = }\frac{mass\text{ of body fat}}{77\text{ kg}}*100 \\ \\ Clearing\text{ the equation: } \\ \\ mass\text{ of body fat = }\frac{3.0\text{ }}{100}*77\text{ kg = 2.31 kg} \end{gathered}`

Now, we can use the conversion factor to convert the kg to pounds:

`2.31\text{ kg * }\frac{2.20462\text{ lb}}{1\text{ kg}}=\text{ 5.0927 lb }\approx\text{ 5.1 lb}`

Then, these athletes have 5.1 lb of body fat on average.