Factoring Numbers on the ISEE

All Levels

LESSON GOAL: Be able to factor any number on the ISEE within seconds.

ISEE Question: How many different factors does 48 have?

Solution: We’re going to solve this using the factor tree method (for a different way of doing it, see the “Prime Factors and Prime Factorization on the ISEE” lesson).

Write 48 in an empty margin and then “branch it” to two numbers that multiply to get 48.

Repeat STEP 1 for any number that has smaller factors (don’t bother dividing by 1).

STEP 3: Circle all the prime factors.

(NOTE that there are many possible factor trees, but you always get the same results because this is math!)

STEP 4: Find all possible products of the circled numbers ( , etc.). Finally, count all factors (don’t forget to include 1 and the number itself!).

Answer: 48 has ten factors and they are 1, 2, 3, 4, 6, 8, 12, 16, 24, 48.

Helpful Tip: A neat way to double-check that you have all numbers is to multiply the first and last, second and second-to-last, third and third-to-last and so on until you reach the middle. All of these products should give the original number!

For other ISEE math concepts, visit