A fraternity is to elect a president and a treasurer from the group of 40 members. How many ways can two officers be elected?

Question

pphalke · Answer

I get 1600 when I multiply but its 1,560 right

welshfella · Answer

Are you familiar with permutations and combinations?

Do you know what 40C2 means?

pphalke · Answer

not too familiar I have read about those but not really familiar

welshfella · Answer

40C2   =  40 * 39
                ------
                    2 * 1

40C2 means the number of combinations of out of 40

welshfella · Answer

- thats a quick way of calculating them   

The full formula is

nCr               n!
                --------
                r!   (n-r)!

welshfella · Answer

with quick method   if  we need number of combination of 4 in 10  it will be

  10*9*8*7
  --------
     4*3*2*1



Do you see the pattern?

pphalke · Answer

yes I do

welshfella · Answer

- you insert 4 multiplications down from 10

then starting from 4  multiply down to 1

welshfella · Answer

so  your answer will be    40*39  /  2