Work together for a fixed time, then one leaves or joins (or a pipe is closed or opened): time for the rest

1. A.
   90/17 hours
2. B.
   89/12 hours
3. C.
   90/13 hours
4. D.
   92/11 hours

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1. A.
   10 days
2. B.
   8 days
3. C.
   12 days
4. D.
   7 days

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1. A.
   3 p.m.
2. B.
   11 a.m.
3. C.
   1 p.m.
4. D.
   2 p.m.

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1. A.
   $44\frac{4}{9}$
2. B.
   $39\frac{4}{9}$
3. C.
   $41\frac{4}{9}$
4. D.
   $43\frac{4}{9}$

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1. A.
   4
2. B.
   3
3. C.
   6
4. D.
   2

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1. A.
   10:16 a.m.
2. B.
   10:22 a.m.
3. C.
   10:48 a.m.
4. D.
   10:18 a.m.

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1. A.
   $\frac{6}{7}$ hours
2. B.
   $\frac{2}{6}$ hours
3. C.
   $\frac{3}{5}$ hours
4. D.
   $\frac{9}{2}$ hours

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1. A.
   $7\frac{1}{3}$ days
2. B.
   $8\frac{2}{5}$ days
3. C.
   $9\frac{1}{5}$ days
4. D.
   $5\frac{1}{2}$ days

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1. A.
   $5\frac{1}{3}$ days
2. B.
   $2\frac{3}{4}$ days
3. C.
   $1\frac{1}{5}$ days
4. D.
   $8\frac{6}{7}$ days

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1. A.
   12 days
2. B.
   10 days
3. C.
   8 days
4. D.
   6 days

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