Answer:
The length of Mai's bike ride was 2.1 times the length of Noah's ride.
Explanation:
Mai biked 5 1/4 miles today
So he biked, in miles:

Noah biked 2 1/2 miles.
So, in miles, he biked:

How many times the length of Noah’s bike ride was Mai’s bike ride?
We divide the Mai distance by Noah's distance. In a division of fractions, we multiply the numerator by the inverse of the denominator. So

The length of Mai's bike ride was 2.1 times the length of Noah's ride.