Question

which of these has the LEAST number of factor pairs?

A.6
B.9
C.18
D.19

Answer 1

6 = 1 x 6, 2 x 3
9 = 1 x 9, 3 x 3
18 = 1 x 18, 2 x 9, 3 x 6
19 = 1 x 19.
Your answer is D.) 19.

Answer 2

d, because 19 is a prime number, so it's only factor pair is 19 and 1