Two pipes A and B can separately fill a cistern in 60 min and 75 min respectively. There is a third pipe in the bottom of the cistern to empty it. If all the three pipes are simultaneously opened, then the cistern is full in 50 min. In how much time, the third pipe alone can empty the cistern ?

Clearly, if A runs 600 meters, B runs = 540 m.
? If A runs 400 m, B runs = 540 x 400 / 600 = 540 x 4 / 6 = 90 x 4 = 360 m
Again, when B runs 500 m, C runs = 450 m
? When B runs 360 m, C runs = 450 x 360 / 500 = 45 x 36 / 5 = 9 x 36 = 324 m.
? A beats C by 400 - 324 = 76 m.

36.98276421 x 21.00002
Using nearest value in whole number for 36.9827421 is 37 and 21.0002 is 21
? 37 x 21 = 777 ? 775

    = Unit digit in [(4²)⁸⁹⁶ x 4]

    = Unit digit in (6 x 4) = 4

Unit digit in (625)³¹⁷ = Unit digit in (5)³¹⁷ = 5

Unit digit in (341)⁴⁹¹ = Unit digit in (1)⁴⁹¹ = 1

Required digit = Unit digit in (4 x 5 x 1) = 0.

(A's speed) : (B's speed) = √b : √a = √16 : √9 = 4 : 3.

Unit digit must be 0 or 5 and sum of digits must be divisible by 9.

Among given numbers, such number is 202860.

Then, x = 7589 - 3434 = 4155

At 11 : 50 A.M. from the formula here P = 11 and Q = 50 so required angle is 11 x 50/2 - 30 x 11 = 275 - 330 = -55 or ignoring the negative sign the required angle is 55°