Algebra II
posted by Trista .
John can clean an attic in 11 hours. DeShawn can clean the same attic in 17 hours. If they worked together how long would it take them? Please solve and show the work. Rounding the answer to the nearest hundredth.

I no the answer is 6.68. I can't remember how to get this.

work with the amount of job done in one hour. In one hour,
John does 1/11
DeShawn does 1/17
together, they do 1/11 + 1/17 = 28/187
so, to do the whole job, they need 187/28 = 6.68
In general, if there are several people taking a,b,c,... hours to do the job, then working together they can do the job in N hours, where
1/N = 1/a + 1/b + 1/c + ...