What is the LCD of #2/15# and #7/10#?

1 Answer
Oct 15, 2016

#LCD = 30#

Explanation:

The LCD, or Lowest Common Denominator is the same as the LCM - the Lowest Common Multiple of the denominators.

You need to find the LCD when you are adding or subtracting fractions, or even when comparing them.

The quickest is start with the bigger denominator and think through its multiples until you get to one which is also a multiple of the other denominator(s).

In this case, the multiples of 15 are: #15, 30, 45, 60, 75, 90....#
Of these, #30, 60, 90 ... #are divisible by 10, but #30# is the lowest.

A longer method would be by using the prime factors:

#15 = " " 3xx5#
#10 = 2" "xx5#

LCD = #2xx3xx5 = 30##