SAT Question 2afd3cec: Percentages answer and explanation with Desmos solution

Choice B is correct. It's given that $20\%$ of the original number of marbles were removed from the group. Let $x$ represent the original number of marbles in the group. It follows that $\frac{20}{100}x$, or $0.20x$, marbles were removed from the group. Therefore, $x-0.20x$ marbles remained in the group. It's also given that $360$ marbles remained in the group. Thus, $x-0.20x=360$, or $0.80x=360$. Dividing both sides of this equation by $0.80$ yields $x=450$. Substituting $450$ for $x$ in the expression $0.20x$ yields $0.20(450)$, or $90$. Therefore, $90$ marbles were removed from the group.