Question

Use the letters a, b, c, d, e, and f. write all possible selections of three letters that can be formed from the letters. (the order of the three letters is not important. enter your answer as a comma-separated list of three-letter combinations. the order of these sets of letters is not important.)

Answer 1

There are 6C3 = 20 such combinations.
abc, abd, abe, abf
acd, ace, acf, ade
adf, aef, bcd, bce
bcf, bde, bdf, bef
cde, cdf, cef, def