Answer
6 ways
Work Step by Step
The order of the chosen shirts does not matter.
Combinations, ${}_{n}C_{r}=\displaystyle \frac{n!}{(n-r)!r!}$
${}_{4}C_{2}=\displaystyle \frac{4!}{(4-2)!2!}=\frac{4\times 3}{1\times 2}=$ 6 ways
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