2021 Fall AMC 10A Problems/Problem 2

Problem

Menkara has a $4 \times 6$ index card. If she shortens the length of one side of this card by $1$ inch, the card would have area $18$ square inches. What would the area of the card be in square inches if instead she shortens the length of the other side by $1$ inch?

$\textbf{(A) } 16 \qquad\textbf{(B) } 17 \qquad\textbf{(C) } 18 \qquad\textbf{(D) } 19 \qquad\textbf{(E) } 20$

Solution

We construct the following table: $\begin{array}{c||c|c||c} & & & \\ [-2.5ex] \textbf{Scenario} & \textbf{Length} & \textbf{Width} & \textbf{Area} \\ [0.5ex] \hline & & & \\ [-2ex] \textbf{Initial} & 4 & 6 & 24 \\ \textbf{Menkara shortens one side.} & 3 & 6 & 18 \\ \textbf{Menkara shortens other side instead.} & 4 & 5 & 20 \end{array}$ Therefore, the answer is $\boxed{\textbf{(E) } 20}.$

~MRENTHUSIASM

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2021 Fall AMC 10A Problems/Problem 2

Problem

Solution