Given
We know the signal requires
The number of flags possible for upper flag is
Now as one of the flag is taken, the number of flags remaining for lower flag in the signal is
The number of ways in which signal can be given
Given
We know the signal requires
The number of flags possible for upper flag is
Now as one of the flag is taken, the number of flags remaining for lower flag in the signal is
The number of ways in which signal can be given