Question

Which equation correctly multiplies only prime numbers and has a product of 18?
a. 2 x 9=18
b.3 x 3 x 3=18
c. 2 x 2 x 3=18
d.2 x 3 x 3=18?

Answer 1

a prime number  has no factors other than itself or 1.

eg 3 is a prime number but 9 is not because 9 = 3*3.

so a is incorrect 
the other 3 options all contain prime numbers but only one multiplication is correct