A walkthrough with 3 examples about how to find the LCD of multiple fractions.
Write each denominator as a product of its prime factors, so: 15=3∙5 and 35=5∙7
List the shared factors each once and any leftover factors each once.
For example 15 and 35 share 5 as a factor, so I write 5 once and include the left over factors 3 and 7 in my LCD each once.
The LCD is 5∙3∙7=105
Therefore 105 is the smallest number that both 15 and 35 go into as factors.
This means I want to write both fractions with 105 in the denominator.
I can’t, however, just change it… I have to multiply by 1 and we need to write that 1 in the form of a specific fraction such as: 2/2,3/3,4/4,5/5,6/6,7/7…
The hard part is, we have to determine the number we want so we can pick the correct fraction to multiply by.