Consider that the number of ways of selecting 'r' objects from 'n' distinct objects is given by,
[tex]^nC_r=\frac{n!}{r!\text{ }.\text{ (n-r)!}}[/tex]There are total 6 countries, out of which 4 is to be selected for the trip.
This means that 2 of the 6 countries have to be skipped.
So the number of ways of selecting 2 countries from 6 countries wull be,
[tex]\begin{gathered} ^6C_2=\frac{6!}{2!\text{ }.\text{ (6-2)!}} \\ ^6C_2=\frac{6\times5\times4!}{(2\times1)\times(4!)} \\ ^6C_2=15 \end{gathered}[/tex]Thus, there are 15 ways to select 2 countries which are needed to be skipped.
Therefore, the second option is the correct choice.
