Three postal workers can sort a stack of mail in 20 ​minutes, 25 ​minutes, and 100 ​minutes, respectively. Find how long it takes them to sort the mail if all three work together.

Answer 1

Let A,B, & C be the 3 workers and they have 1000 pieces of mail to sort.

Then Worker A's rate is 1000 pieces/20 min = 50 pieces/min

and Worker B's rate is 1000 pieces/25 min = 40 pieces/min

and Worker C's rate is 1000 pieces/100 min = 10 pieces/min

Working together, they can sort at 50 + 40 + 10 = 100 pieces/min

Then, 1000 pieces/100 pieces/min = 10 minutes