kat187 wrote:hi your a little more advanced in the brain than I.
can you explain the factorial process you have for the
combination's for the committee of 3 senior to 1 junior
you have 6!/3! 3!
then for the other you have
only 4!/3!
please explain
mj41 wrote:Should the formula not be n!/r!(n-r)!
yes, the formula is indeed the one that you have written.
kat187,
dmateer25 has already shown you the correct way, how nCr formula works.
But, here is a shortcut to get this value, without bothering much about factorials.
Here it goes ....
Suppose you have to find nCr ( or you have to SELECT r things out of n) :
for the numerator, write the product of r consecutive integers, beginning with n, each 1 less than the previous.
for the denominator, write the product of r consecutive integers beginning with 1, each 1 more than the previous.
For e.g calculate 6C3 :
step 1 : for the numerator, write the product of 3 consecutive integers, beginning with 6, each 1 less than the previous.
= 6 * 5 * 4 ( don't simplify. Let it be as the way it is).
step 2 : for the denominator, write the product of 3 consecutive integers beginning with 1, each 1 more than the previous.
= 1 * 2 * 3
therefore the value of 6C3 is numerator/denominator = (6 * 5 * 4) / (1 * 2 * 3) = 20
similarly, 4C2 = ( 4 * 3) / (1 * 2) = 6
hope it becomes easier for you now!
