explain LCD

Question

Explain using pictures what we do when we find the LCD between 3 and 7. 

Answer 1

If you are looking for the LEAST COMMON DENOMINATOR in order to simplify something like 1/3 + 4/7, then the process is to examine the FACTORS of those denominators. Those denominators, 3 and 7, are relatively prime (HAVE NO FACTORS IN COMMON), so the selected LCD must be 3•7, which is 21.

 

I have no idea why the instructions are telling you to use pictures!  (In my opinion, that's the kind of nuttiness that we're seeing a lot of in this CommonCore era.)

 

BTW: 1/3 + 4/7 would be 7/21 + 12/21 = 19/21.