How do you do a factor tree for 42?

Answer 1

Start by breaking 42 into any of its factors. I like to start by using factors I know are prime. In this case, I'll begin with 2 and 21.

42

(This is the number we began with)

2*21=42

(2 is always an easy prime factor for any even number)

2*3*7=42

(21=3*7. Both 3 and 7 are prime, so were done.)