A can paint a house in 42 days and B can do it in 21 days. Along with C, they can finish the job in 7 days only.C alone can do the painting job in how many days, ?
Let the total work = LCM of 42 & 21 = 42 units
A's efficiency = 42/41 = 1
B's efficiency = 42/21 = 2
efficiency of A+B+C = 42/7 = 6
1+2+efficiency of C = 6
efficiency of C = 6-3 = 3
C alone can complete the work in 42/3 = 14days
So the answer is option C.
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