p is twice as fast as q and r together. workings together all 3 can do a work in 21 days. in how many days can q and r together do the work??

let us say p,q and r are efficiencies of P, Q and R. (p+q+r)(21) = 1 work, given that p = 2(q+r), this implies 3(q+r)(21)= 1W. To do the same amount of work (q+r)(no. days) = 1W = 3(q+r)(21). On solving we get, number of days = 63 Hope that helps. Cheers