A 4mL of blood contains 7.2 mg of cholesterol what is the mg% of cholesterol

Answer 1

In order to answer this question, you need to know the density of blood so that you can convert ml of blood to mg of blood. There should be a density chart in the book.

You need to know the mg of blood because the mg% is going to be the mg of cholesterol divided by the mg of blood and then multiplied by 100%.

I googled the density of blood and it's pretty close to the density of water: 1.05 g/mL

Starting with the 4 mL of blood convert to mg using the known conversion factors:

4 mL x (1.05 g / 1 mL) x ( 1000 mg / 1 g) = 4200 mg

the mL's cancel top and bottom and so do the g's so your left with mg.

Now you need to do the division

mg% = (mg cholesterol / mg blood) x 100%

= (7.2 mg / 4200 mg) x 100% = 0.1714285714%

Now for the sig. figs.

4 mL is an exact number so we don't use it.

7.2 mg has 2 significant figures so our answer needs to have 2 sig. figs.

= 0.17%