A, B and C together finish a work in 4 days if A alone can finish the same work in 8 days and B in 12 days. Find how long will C take to finish the work?


Given: 

A, B and C together finish a work in 4 days.

A alone can finish the work in 8 days and B in 12 days.

To find: Here we have to find how long will C take to finish the work.

Solution:

We would consider total work to be  1

Work done by A in one day = $\frac{Total work}{Total number of days taken}$

Work done by A in one day = $\frac{1}{A}$

Work done by A in one day = $\frac{1}{12}$


Similarly, work done by B and C is $\frac{1}{18}$ and $\frac{1}{C}$ respectively.

Therefore,

Total work done by all three in one day = $\frac{1}{12}\ +\ \frac{1}{18}\ +\ \frac{1}{C}$

Work done in one day $\times$ Total number of days = Total work

$[\frac{1}{12}\ +\ \frac{1}{18}\ +\ \frac{1}{C}]\ \times\ 4\ =\ 1$

$\frac{1}{12}\ +\ \frac{1}{18}\ +\ \frac{1}{C}\ =\ \frac{1}{4}$

$\frac{1}{C}\ =\ \frac{1}{4}\ -\ \frac{1}{12}\ -\ \frac{1}{18}$

$\frac{1}{C} \ =\ \frac{9\ -\ 3\ -\ 2}{36}$

$\frac{1}{C} \ =\ \frac{4}{36}$

$\frac{1}{C} \ =\ \frac{1}{9}$


C = 9 days



So, C can complete the same work in 9 days.

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Updated on: 10-Oct-2022

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