Let suppose x = y x = y xy = x*x xy + x*x = x*x + x*x xy + x*x = 2x*x xy + x*x - 2xy = 2x*x - 2xy x*x - xy = 2x*x - 2xy 1(x*x - xy) = 2(x*x - xy) 1 = 2 1 + 2 = 2 + 2 1 + 2 = 4
If repetition of numbers is not allowed then how many numbers of five digits can be formed by using 1,2,3,4,5. If 4 is necessarily taken at hundred's place and 2 is not allowed at unit's place
3 pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the tank in 1 day?