**Tips:-**

**1-**If

**given**

**the time it takes a pipe to fill or empty a tank the reciprocal of the time will represent that part of the tank that is filled or emptied in unit time.**

**2-**The amount that a pipe can fill or empty in unit time is its rate.

**3-**If given the part of a tank that a pipe or a combination of a pipes can fill or empty in unit time invert the part to find the total time required to fill or empty the whole tank.

**4-**To solve the tank problems in which only one action (filling or emptying) is going on:

a) Invert the time of each pipe to Tfink how much each can do in unit time.

b)Add the reciprocals to find how much all can do in unit time.

c)Invert the sum to find the total time.

**5-**In problems in which both filling and emptying actions are occurring.

a)Determine which process has the faster rate.

b)The difference between the filling rate and the emptying rate is that part of the tank that is actually being filled or emptied in unit time.The frit action representing the slower action is subtracted from the fraction representing the faster process.

c)The reciprocal of this difference is the time it will take to fill or empty the tank.

**Example:-**

**Twenty men can finish a piece of work in 30 days.When should 5 men leave the work so that is may be finished in 35 days?**

**Solution:-**

**20 men can do work in 30 days i.e one man can do it in 600 days.**

Let 5 men leave after x days i.e, 20 men do the work for x days and thereafter only 15 men do the remaining work in (35-x) days.

: 20x + 15(35-x) = 600

Hence 5 men should leave after 15 days.

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