A pilot and copilot for a space flight are to be chosen from a group of 5 men of different ages. If the older

Question

A pilot and copilot for a space flight are to be chosen from a group of 5 men of different ages. If the older man must always be the pilot, how many different crews can be made up?

Answer 1

10

Answer 2

5 choose 2 ?  

5!/(2!*(3!)) / 2

http://en.wikipedia.org/wiki/Combination

http://en.wikipedia.org/wiki/Permutation

the last divided by two since the can be drawn in any order, there must be duplicates pairs, meaning only one can be older..

more intuitively, choose any one (5 ways) then choose another (4 ways) = 20 ways, then order them / 2 = 10

Answer 3

Not sure how to read your question - if THE older man always has to be the pilot, there can only be 4 different crews made up (the eldest of the 5, then either of the other 4).

If, however, you mean the oldest one of the 2 chosen has to be the pilot, then there are 9 different crews can be made up.

So my answer depends - either 4 or 9.