Question

Street sweeping vehicles can clean 3 miles of streets per hour. A city owns two street sweepers, and each sweeper can be used for three hours before it comes in for an hour to refuel. During an 18-hour shift, how many miles of street can be cleaned?

Answer 1

We know that
In a period of 4 hours (3 hours of work and 1 hour to refuel)
each street sweepers clean------> 3 miles*3 =9 miles

divide 18 hours by 4
18/4=4.5
4.5 is equal to 4 periods of 4 hours plus 2 hours

Multiply 4 by 9 miles
4*9=36 miles

in the period of 2 hours (in this period there is no refuel)
3*2=6 miles

each street sweepers clean in 18 hours-----> (36+6)-----> 42 miles
two street sweepers clean in 18 hours=2*42------> 84 miles

the answer is
84 miles