A and B undertook to do a piece of work for Rs. 48,000. A could do it alone in 5 days and B could do it alone in 8 days. With the help of C…

Work done by A in 1 day = 1/5

Work done by B in 1 day = 1/8

Let the work done by D in 1 day be 1/x

⇒ Work done by C in 1 day = 2/x (Given)

⇒ Work done by all in 1 day$(= \frac{1}{5}\; + \;\frac{1}{8}\; + \;\frac{1}{x}\; + \;\frac{2}{x})$

Now, when all of them work, they finish the work in 3 days.

⇒ Work done by all in 1 day = 1/3 $(\begin{array}{l} \frac{1}{5}\; + \;\frac{1}{8}\; + \;\frac{1}{x}\; + \;\frac{2}{x}\; = \;\frac{1}{3}\\ \frac{3}{x}\; = \;\frac{1}{3} - \frac{1}{5} - \frac{1}{8}\; = \;\frac{{40 - 24 - 15}}{{120}}\; = \;\frac{1}{{120}} \end{array})$

⇒ x = 120 × 3 = 360

Time taken by C = 180 days

⇒ A’s total payment = 48000 × (3/5) = 28800

⇒ C’s total payment = 48000 × (3/180) = 800

∴ Difference = 28800 - 800 = 28000