Question

• Suppose two species of cicada appear in the same year. If one species comes out every 7 years and the other comes out every 13 years, how many years will go by before the species appear at the same time again? Explain. their using prime numbers for when cicadas come out and factors of 4,7,8 and13

Answer 1

91 years

Explanation:

Two species of cicada appear in the same year.

One species comes out every 7 years.

Other comes out every 13 years.

Find the lowest common multiple of numbers 7 and 13. These two numbers both are prime numbers, so

`LCM(7,13)=7\cdot 13=91`

This means 91 years will go by before the species appear at the same time again.