Question 1023274
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{{{C[20]^5}}} = {{{(20*19*18*17*16)/(1*2*3*4*5)}}} = 19*6*17*8 = 15504,


the number of combinations of 20 things taken 5 at a time.


See the lesson <A HREF=http://www.algebra.com/algebra/homework/Permutations/Introduction-to-Combinations-.lesson>Introduction to Combinations</A> in this site.