There are two pumps to fill a tank with water. First pump can fill the empty tank in 8 hours, while the second in 10 hours, If both the pumps are opened at the same time and kept open for 4 hours, the part of the tank that will be filled up is :
Part of the tank filled in an hour by both pumps
∴ Part of the tank filled in 4 hours
Hence option [C] is correct answer.