P, Q and R can do a work in 15, 20 and 30 days respectively. The contractor decides to put any two of them on the job so as to finish the work earlier. Which of these choices is the best?
P = 15 days
Q= 20 days
R = 30 days
Total work = lcm (15,20,30)= 300 days
(P )'s effiency = $$300\div15$$ =20
(Q)'s effiency = $$300\div20$$ =15
(R)'s efficiency = $$300\div 30$$ = 10
P and Q efficiency is more than R
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