Question

A farmer can plow a given field in 7 hours. If his son helps him, they can plow the field together in 4 hours. How long would it take his son to plow the field alone? Express your answer as a fraction reduced to lowest terms, if needed.

Answer 1

If the son takes x hours,

1/7 + 1/x = 1/4

Answer 2

10

Answer 3

28/3