Mr. A has a set of $4$ distinct t-shirts. Since it is winter he has to wear $3$ t-shirts everyday to beat the cold. How many distinct arrangements of t-shirts can he wear anyday? (Here is he has t-shirts $a$,$b$,$c$ and $d$ then wearing $a$ inside of $b$ which is inside $c$ is different than wearing $c$ inside of $b$ which is inside of $a$.
Clearly this question just involves choosing three t-shirts and finding out their permutations. This can be done in ${4 \choose 3} \cdot 3! = 24$ ways. But the source from which I got this question from has the answer as $48$. Am I going wrong somewhere?
I suspect that the source meant that he needs to wear at least $3$ T-shirts. That's $24$ arrangements of $3$ T-shirts, as you calculated, and another $4!=24$ arrangements of all $4$ T-shirts.