Brian can lay a slab of concrete in 6 hours, while Greg can do it in 4 hours. If Brian and Greg work together, how long will it take?

Answer:2 2/5 hoursStep-by-step explanation:In 6 hours Brian can lay 1 slab of concretedividing both side by 6 in 6/6 hours Brian can lay 1/6 slab of concreteThus, in 1 hour  Brian can lay 1/6 slab of concreteIn 4 hours Greg can lay 1 slab of concretedividing both side by 4 in 4/4 hours Greg can lay 1/4 slab of concreteThus, in 1 hour  Greg can lay 1/4 slab of concreteThus, total part of slab laid by both in 1 hour when they work together1/6 + 1/4 = 4+6/(6*4) = 10/24 = 5/125/12 of slab of concrete is laid by both of them in 1 hourtime taken to lay 5/12 of slab = 1 hourdividing both side by 5/12time taken to  5/12/ 5/12 of slab = 1/5/12 hour = 12/5 hourstime taken to 1/1 of slab = 12/5 hours = 2 2/5 hoursThus,it takes 2 2/5 hours to lay the full slab of concrete when Brian and Greg work together,