Father can do the job on the farm in 6 hours. The older son can do it in 8 hours. The younger son can do same job in 12 hours. How long will it take them to do the job, if they all work together?

Answer: it will take a combined rate of 2.67 hoursStep-by-step explanation:Father can do the job on the farm in 6 hours. This means that the father's unit rate of working will be 1/6The older son can do it in 8 hours. This means that the older son's rate of working will be 1/8The younger son can do same job in 12 hours. This means that the younger son's working rate is 1/12When they work together, they will be working simultaneously. It means that their unit rates are additive. The combined unit rates will be 1/6 + 1/8 + 1/12 = (20 + 15 + 10)/12045/120Assuming it takes t hours for them to complete the work while doing it together. Their combined unit rate will be 1/t45/120 = 1/t45t = 120t = 120/45 = 2.67 hours