9 students can make a poster in 10 hours. How many students should join them so that they altogether can make this poster in 6 hours?

Answer 1

9 can do the work in 10 hours

how many can do the work in 6 hours? 15

6 more students need to join the 9 to get 15

IF 9 do it in 10, then a student working alone would do it in 90 hours

2 students could do it in 90/2 = 45 hours

3 students 90/3 = 30 hours

6 students 90/6 = 15 hours

15 students 90/15 = 6 hours