The task is to generate the correct answer for a given math problem.

[EX Q]: Problem: two pipes can fill the cistern in 10 hr and 12 hr respectively , while the third empty it in 30 hr . if all pipes are opened simultaneously , then the cistern will be filled in
[EX A]: 6.67 hr

[EX Q]: Problem: the average age of 10 men is increased by years when two of them whose ages are 21 years and 23 years are replaced by two new men . the average age of the two new men is
[EX A]: 3

[EX Q]: Problem: the slant height of a cone is 35 cm and radius of the base is 14 cm , find the curved surface of the cone .
[EX A]:
1540', 'd ) 1500', 'e ) 6100'