Four boys and ten girls can cut a field in 5 hours if the boys work at (frac{5}{4}) the rate at which the girls work. How many boys will be needed to cut the field in 3 hours?

A.
180 
B.
60 
C.
25 
D.
20
Correct Answer: Option D
Explanation
Let x represents number of boys that can work at (frac{5}{4}) the rate at which the 10 girls work
For 1hr. x boys will work for (frac{frac{1}{5}}{4}) x 10
x = (frac{4}{5}) x 10 = 8 boys
8 boys will do the work of ten girls at the same rate 4 + 8 = 12 boys cut the field in 5 hrs
For 3 hrs, (frac{12 times 5}{3}) boys will be needed = 20 boys