Question

6th grade math

Drusilla replaces the light bulb in the hall closet every 9 months and replaces the air filter every 6 months. She just replaced both items this month. After how many months will she replace both the light bulb and the air filter?

Answer 1

They will both be replaced the 18th month.

Answer 2

She will replace both at the same time in 18 months

Explanation:

The first thing you have to do to find when she will change them at the same time, is to try with multiples of both, untill they match.

Hall Closet = every 9 months

Air Filter = every 6 months

1) 9-18-27-36-45

2)6-12-18

We find that in the 18th month he will change both of them.