JAMB - Mathematics (1987 - No. 10)
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?
180
60
25
20
Giải thích
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
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