Subject: Math Fractions
Name: Paulette
Who are you: Parent (Elementary)

please show me easy way to show my son in 5th grade how do understand Least Common Denominator
Why is the LCD of 3/4 and 4/8 not the product of 4 and 8?
thank you for your help

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