NEED HELP WITH FINDING A PATTERN

Question

Question: Two frogs live together in a pond. Frog one croaks every 4 minutes and frog two croaks every 2 and 1/2 minutes. If they both croak together at 11 am, what is the first time after 1 pm that they will croak together?

Answer 1

Least common multiple of 2.5 and 4 is 20

4(5) = 20

2.5(8) = 20

 

You can see this if you list the multiples out:

2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20

4, 8, 12, 16, 20

 

Every 20 minutes they will croak at the same time

11:00

11:20

11:40

12:00

12:20

12:40

1:00

1:20

 

The first time AFTER 1:00 that they croak together is at 1:20 pm