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2021 AMC 10B Problem 21

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2021 AMC 10B Problem 21AMC 10 Step by Step

Name: Date: September 13, 2026

Transformations & Symmetry · difficulty 4 of 5 · about 6 min · position P21-25

A square piece of paper has side length $1$ and vertices $A,B,C,$ and $D$ in that order. As shown in the figure, the paper is folded so that vertex $C$ meets edge $\overline{AD}$ at point $C'$ , and edge $\overline{AB}$ at point $E$ . Suppose that $C'D = \frac{1}{3}$ . What is the perimeter of triangle $\bigtriangleup AEC' ?$

A)
$2$
B)
$1+\frac{2}{3}\sqrt{3}$
C)
$\frac{13}{6}$
D)
$1 + \frac{3}{4}\sqrt{3}$
E)
$\frac{7}{3}$

2021 AMC 10B Problem 21

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