Multiple choice

P and Q can do a piece of work in 12 days, Q and R can do a piece of work in 15 days and R and P can do a piece of work in 20 days. Q alone can do the whole work in

  1. 40 days

  2. 25 days

  3. 20 days

  4. 30 days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Work rates: (P+Q)=1/12, (Q+R)=1/15, (R+P)=1/20. Adding all 3 equations: 2(P+Q+R)=1/12+1/15+1/20=12/60 → P+Q+R=1/10. Q = (P+Q+R)-(R+P)=1/10-1/20=1/20. So Q alone takes 20 days.

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