Three pipes A, B and C can fill a tank in 6 hours. After working together for 2 hours, C is closed and A and B can fill the remaining part in 7 hours. The number of hours taken by C alone to fill the tank is



[ A ]    10 hrs.
[ B ]    12 hrs.
[ C ]    14 hrs. right
[ D ]    16 hrs.
Answer : Option C
Explanation :
Part filled in 2 hours = $2 \over 6$ = $1 \over 3$

Remaining part = 1 - $1 \over 3$ = $2 \over 3$

So,(A+B) ;s 7 hours's work = $2\over 3$

So,(A+B);s 1 hour's work = $2 \over 21$

C's1 hour's work =(A+B+C)'s

One hourr's work -(A+B)'s one

hour's work = ($1 \over 6$ - $2 \over 21$) = $1 \over 14$

C alone can fill the tank in 14 hours

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