Multiple choice

P and Q together complete a work in 8 days. Q and R together complete a work in 16 days and R and P together complete the same work in 8 days. In how many days P, Q and R together can complete the wok?

  1. 7.1

  2. 7.2

  3. 6.4

  4. 5.8
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let P+Q = 8, so (P+Q)'s work = 1/8 per day. Q+R = 16, so (Q+R)'s work = 1/16 per day. R+P = 8, so (R+P)'s work = 1/8 per day. Adding all three equations: 2(P+Q+R) = 1/8 + 1/16 + 1/8 = 5/16, so P+Q+R = 5/32. Time for all three = 32/5 = 6.4 days.

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