Chapter 4 - Proportions, Percents, and Solving Inequalities - 4.1 - Ratios and Proportions - Problem Set 4.1 - Page 149: 47

$n=50$

Using cross-multiplication, the value of the variable that satisfies the given equation, $ \dfrac{n}{150-n}=\dfrac{1}{2} ,$ is \begin{array}{l}\require{cancel} 2(n)=1(150-n) \\\\ 2n=150-n \\\\ 2n+n=150 \\\\ 3n=150 \\\\ n=\dfrac{150}{3} \\\\ n=50 .\end{array}