problem 7 calculate each percentage mentally. \( \begin{array}{lll}\text { a. } 25 \% \text { of } 400 & \text { b. } 50 \% \text { of } 90 & \text { c. } 75 \% \text { of } 200 \\ \text { d. } 10 \% \text { of } 8,000 & \text { e. } 5 \% \text { of } 20\end{array} \)

To tackle these percentages mentally, you can break them down into simpler steps: For \( 25\% \) of \( 400 \), you can think of it as \( \frac{1}{4} \) of \( 400 \), which equals \( 100 \). For \( 50\% \) of \( 90 \), you're simply finding half, which is \( 45 \). When calculating \( 75\% \) of \( 200 \), it's like taking \( 3/4 \) of \( 200 \), giving you \( 150 \). Moving on, \( 10\% \) of \( 8,000 \) is straightforward; just move the decimal one place to the left, resulting in \( 800 \). Finally, \( 5\% \) of \( 20 \) can be found by calculating \( 1\% \) first as \( 0.2 \), and then multiplying by \( 5 \), resulting in \( 1 \). So there you have it! The answers are: a. 100 b. 45 c. 150 d. 800 e. 1