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A alone can paint a wall in 50 days and B alone can do it in 10 days. If A, B and C together can paint the wall in 6.25 days, then in how many days can C alone paint the wall?

A alone can paint a wall in 50 days and B alone can do it in 10 days. If A, B and C together can paint the wall in 6.25 days, then in how many days can C alone paint the wall? Correct Answer 25

Given:

A can paint in = 50days, B can paint in = 10days, A + B + C can paint in = 6.25days

Let the total work be 100units

Calculation:

Efficiency of A = 100units/50days = 2units/day

Efficiency of B = 100units /10days = 10units/day

Efficiency of A + B + C = 100units/6.25days = 16units/day

If, A + B work together,

Then Efficiency of A + B = (2 + 10) units/day = 12units/day

Now, subtract efficiency of A + B from efficiency of A + B + C

⇒ 16units/days – 12units/day = 4units/day

∴ Efficiency of C = 4units/day

C alone can paint the wall = 100/4 = 25days 

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