Question

Three postal workers can sort a stack of mail in 35 ​minutes, 30 ​minutes, and 210 ​minutes, respectively. Find how long it takes them to sort the mail if all three work together.

The time it takes for all three to complete the job is ___ minutes.

Answer 1

92 minutes

Explanation:

Find the average of the numbers by adding them all together, then dividing the sum by three.

Answer 2

The time it takes for all three of them to complete the job is 15 minutes.

Explanation:

Three postal workers can sort a stack of mail in 35 minutes, 30 minutes and 210 minutes respectively .

The rate for each person to stack a mail can be represented as

rate1 = 1/35

rate2 = 1/30

rate3 = 1/210

let t = time in minutes

1/35 + 1/30 + 1/210 = 1/t

find the common factor of the denominator

(6 + 7 + 1)/210

14/210 = 1/t

cross multiply

14t = 210

divide both sides by 14

t = 210/14

t = 15

The time it takes for all three of them to complete the job is 15 minutes.