Bunuel wrote:

It takes John exactly 30 minutes to rake a lawn and it takes his son Todd exactly 60 minutes to rake the same lawn. If John and Todd decide to rake the lawn together, and both work at the same rate that they did previously, how many minutes will it take them to rake the lawn?

A. 16

B. 20

C. 36

D. 45

E. 90

Kudos for a correct solution.

Time taken by John to rake a lawn = 30 minutes

The work done by John in 1 min = (1/30)

Time taken by John's Son to rake a lawn = 60 minutes

The work done by John's Son in 1 min = (1/60)

The work done by John and his Son in 1 min = (1/30)+(1/60) = (3/60) = (1/20)

i.e. Time taken by John and his Son together to rake (1/20) of Lawn = 1 min

i.e. Time taken by John and his Son together to rake (1) of Lawn = 1/(1/20) = 20 min

Answer: Option B

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