Joe digs a ditch in 3.2 hours. Joe working with George can did the same length ditch in 2.7 hours. How long would it take George to dig the ditch by himself ? Solution Joe digs a ditch in 3.2 hours...so in 1 hour he digs 1/3.2 ditch=10/32=5/16 let george alone take x hrs to dig the ditch...so in 1 hour he digs 1/x ditch so in 1 hour joe and george together dig 5/16+1/x ditch =(5x+16)/16x so they take 16x/(5x+16) hrs to dig the ditch together but this given as 2.7 hours so 16x/(5x+16)=2.7 cross multiplying we get 16x=2.7(5x+16)=13.5x+43.2 16x-13.5x=43.2 2.5x=43.2 x=43.2/2.5=432/25=17.28 hours so george alone takes 17.28 hrs to dig the ditch.