91Ó°ÊÓ

John, Jim, Jay, and Jack k, each of the boys can play all 4 instruments

We have to find out the number of arrangements if four of them playing different instruments and when John and Jim can play all 4 instruments, but Jay and Jack can each play only piano and drums.

If each of the boys plays all instruments, then using different permutations for 4 different instruments, we get there are $$\begin{gathered} 4!=4×3×2×1 \\ =24 \end{gathered}$$

Since Jay and jack play only piano and drums, then arrangements for them is 2! using different permutations concepts,

John and Jim can play all, but only 2 instruments are left there because of the other two people, hence the arrangement for them is 2!.

Thus possible arrangement when John and Jim can play all 4 instruments, but Jay and Jack can each play only piano and drums is $2!×2!=4$