Hi Paulette,
The reason is the word least.
4 8 = 32 is a common denominator since
^{3}/_{4} = ^{(3 x 8)}/_{(4 x 8)} = ^{24}/_{32} and ^{4}/_{8}= ^{(4 x 4)}/_{(8 x 4)} = ^{16}/_{32}
But ^{4}/_{8} = ^{2}/_{4} and thus 4 is also a common denominator. 4 is less than 32 so 32 is not the least of all possible common denominators.
Penny
