Investigation 2

How can you decide whether finding common multiples or common factors is helpful in solving a problem?

You can decide whether finding the common multiples or common factors by seeing if you have to multiply or find factor pairs. If your aim is to find bigger/greater numbers, than it's probably a common multiple problem. If you have to find a pair of smaller numbers, you probably have to find common factors.

http://www.ixl.com/math/grade-6/gcf-and-lcm-word-problems

For the question above, you have to find the LCM (Lowest Common Multiple) of 4 and 5.

For the 2nd question, you have to find the GCF (Greatest Common Factor) of 20 and 16.