Solution. This appears to be very similar to the example above, but there is a subtle difference

This appears to be very similar to the example above, but there is a subtle difference. The number of ways of selecting a team of five is Let us imagine that the chosen team is ABCDE. Hence the other team would automatically be FGHIJ. However another possible combination of a team of

five would be FGHIJ and this would then automatically select the other team as ABCDE. In other words the calculation picks each pair of teams twice. Hence the actual number of teams is