Three small pumps and a large pump are filling a tank. Each small pump works at 2/3rd the rate of large pump. If all our work at the same time, they should fill the tank in what fractions of the time it would have taken the large pump alone?

Three small pumps and a large pump are filling a tank. Each small pump works at 2/3^rd the rate of large pump. If all our work at the same time, they should fill the tank in what fractions of the time it would have taken the large pump alone?

A 4/7

B 1/3