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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