What is the highest common factor of 90 and 216?

Answer 1

Expressing each number as the product of prime numbers can help in taking out common factor.

Prime factorization of 90 = 2x3x3x5 = 21x32x51

Prime factorization of 216 = 2x2x2x3x3x3 = 23x33

It is clear that 2x3x3 or 21x32 is common in P.F. of both numbers.

So, the highest common factor is 2x3x3 = 18.

Answer 2

90 = 2 x 3 x 3x 5 while 216 = 2 x 2 x 2 x 3 x 3 x 3

The factors common to both numbers are 2 x 3 x 3 = 18

So the HCF is 18