Question

Bob can type 2 letters in 4 hours while bill can do it in six. How many hours will it take them, working together, to type six letters

Answer 1

7 hours and 12 minutes, or 7.2 hours

Answer 2

7hr 12 min

Explanation:

Given that

Bob can type 2 letters in 4 hours

while on the other hand bill can do it in six hours

We need to find out the no of hours in which they type 6 hours

So,

Bob's rate is

= 2 ÷ 4

= 1 ÷ 2 letter per hour

And,

Bill's rate is

= 2 ÷ 6

= 1 ÷ 3 letter per hour

Now

Together rate is

= 1 ÷ 2 + 1 ÷ 3 = 5 ÷ 6 letter per hour

We know that

rate × hours = production

Let us assume the hours be x

So,

(5 ÷ 6)x = 6

x = (6 ÷ 5) × 6

x = 36 ÷ 5

= 7 1 ÷ 5

= 7hr 12 min