Answer: In 36 minutes both buses will end up at the library.
Step-by-step explanation:
Given: Buses from one route stop at the library every 9 minutes.
Buses from the other route stop at the library every 12 minutes.
The number of minutes in which both buses will end up at the library= LCM(9,12)
Now , 9= 3 x 3
12= 2 x 2 x 3
LCM(9,12) = 2 x 2 x 3 x 3 = 36
In 36 minutes both buses will end up at the library.
