Three men working at the same rate can dig a trench, 5m long, in 4hours. Calculate the time that 2 men working at the same rate would take to dig a similar trench, 5m long?
rate in meters/manhour = 5 meters /(3 men*4 hr) = 5/12 m/manhour
time = (12/5) man hr /meter * 5 meter/ 2 man = 12 *5 / (5*2) = 6 hr
or just say 3/2 of 4