Question 2.9: Blood plasma has a density of 1.027 g/mL at 25°C. What volum......

Step 1:    The given quantity is 125 g of blood plasma. The units of the desired quantity are milliliters. Thus our starting point is
\quad\quad\quad\quad125 g = ? mL
Step 2:    The conversion from grams to milliliters can be accomplished in one step because the given density, used as a conversion factor, directly relates grams to milliliters. Of the two conversion factor forms
\quad\quad\quad\quad \frac{1.027  g}{1  mL}\quad\quad and \quad\quad\frac{1  mL}{1.027  g}
we will use the latter because it allows for cancellation of gram units, leaving milliliters.
\quad\quad\quad\quad 125  \cancel{g}\times(\frac{1  mL}{1.027  \cancel{g}})= ? mL
Step 3:    Doing the necessary arithmetic gives us our answer:
\quad\quad\quad\quad (\frac{125\times1}{1.027})  mL = 121.71372  mL \quad\quad\quad (calculator  answer)\\\quad\quad\quad\quad\quad\quad\quad\quad\quad = 122  mL \quad\quad\quad (correct  answer)
Even though the given density contained four significant figures, the correct answer is limited to three significant figures. This is because the other given number, the mass of blood plasma, had only three significant figures.