Question

Five teachers can mark 60 exams papers in 4 hour. How long will it takes 3 teachers to mark all 60 papers?

Answer 1

5 teachers mark 60 papers in 4 hours

1 teacher marks 12 papers in 4 hours
3 teachers mark 36 papers in 4 hours
3 teachers mark 60 papers in 4(60/36) or 6 2/3 hours

Answer 2

3/5 the teachers, so 5/3 the time: 6 hr 20 min

or, since each of the 5 teachers can grade 3 papers per hour,
3 teachers can grade 9 papers per hour, so
60 papers/(9papers/hr) = 20/3 hr = 6 hr 20 min