Question 998322
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Let A = {1, 2, 3, 4, 5, 6}.
(a) How many subsets of 4 elements does the set A have?

(b) How many subsets of A have no more than 3 elements?
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a) {{{C[6]^4}}} = {{{(6*5)/(1*2)}}} = {{{30/2}}} = 15.


b) {{{C[6]^1}}} + {{{C[6]^2}}} + {{{C[6]^3}}} = 6 + 15 + 20 = 41.


Or  42,  if to add the empty subset.


Do you know what  {{{C[n]^m}}}  is?


If not, &nbsp;look into the lesson &nbsp;<A HREF=http://www.algebra.com/algebra/homework/Permutations/Introduction-to-Combinations-.lesson>Introduction to Combinations</A>&nbsp; in this site.