Question
A and B together can do a piece of work in 30 days, B
and C together can do it in 20 days. A starts the work and works on it for 5 days, then B takes it up and works for 15 days. Finally, C finishes the work in 18 days. In how many days can C do the work when doing it separately (in days)?Solution
(A + B)’s 1 day work = 1/30 And (B + C)’s 1 day work = 1/20 Also, A’s 5 days w + B’s 15 days w + C’s 18 days w = 1 work ⇒ A’s 5 days w + B’s 5 days w + B’s 10 days w + C’s 10 day w + C’s 8 day w = 1 work ⇒ (A + B)’s 5 days w + (B + C)’s 10 days w + C’s 8 days work = 1 work ⇒ 5/30 + 10/20 + C’s 8 days work = 1 work ⇒ 1/6 + 1/2 + C’s 8 days work = 1 work ⇒ C’s 8 days work = 1 – ( 1/6 + 1/2 ) work ⇒ C’s 8 days work = 1 – ((1 + 3)/6) = 1 - 4/6 = 1 - 2/3 ∴ C’s 8 days w = 1/3 work ∴ C will complete the work in 8 × 3 = 24 days
35.25 71 146 296 624 1376
...22   39    58    81   ?      141
1 9 64 255 755 1835
...Find the odd one out: 11, 13, 17, 19, 21
32 63 121 ? 453 889
...1,2, 5, ‘?’, 41, 122, 365
7Â Â Â Â Â Â 15Â Â Â Â Â Â Â 31Â Â Â Â Â Â 63Â Â Â Â Â Â 127Â Â Â Â Â Â ?
...122, 116, 125, 119, 128, ?
13, 14, 18, 27, 43, ?
38    40    83    254    ?     5126
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