A small bus interchange has 2 feeder services that start simultaneously at 9am. Bus number 801 leaves the interchange at 15-min intervals, while bus number 802 leaves at 20-min intervals. On a particular day, how many times did both services leave together from 9 am to 12 noon inclusive? plz answer fast !!

Answer :

Given Bus number 801 interchange in interval of 15 minutes and bus number 802 interchange in interval of  20 minutes .

So,

To find how many times both buses leaves together , We find L.C.M. of 15 and 20

So,

L.C.M( 15 and 20 ) =  2 $\times$ 2  $\times$  3  $\times$ 5 = 60

So,

Both buses meet after 60 minutes ,

So,

Both buses leave together at  9: 00 am , 10 : 00 am , 11 : 00 am and 12 : 00 noon .

So,

Four number of times both buses leaves together .                                        ( Ans )