Solution:
Given that there are 150 calories in a cup of whole milk, and 81 in a cup of skim milk.
The percent decrease when switching from a cup of whole milk to skim milk is evaluated as
[tex]\begin{gathered} \text{percent decrease = }\frac{150-81}{150}\times100 \\ =\frac{69}{150}\times100 \\ =0.46\times100 \\ \Rightarrow\text{percent decrease}=46\% \end{gathered}[/tex]
Hence, the percent decrease in the number of calories per cup when switching from whole milk to skim milk is 46%.
