The Lucknow-Indore Express without its rake can go 24 km an hour, and the speed is diminished by a quantity that varies as the square root of the number of wagon attached. If it is known that with four wagons its speed is 20 km/h, the greatest number of wagons with which the engine can just move is  Choose the correct choice from the following
A) 144
B) 140
C) 143
D) 124
E) 142
Solution: Speed = 24- k√n;   Putting the value, n = 4;   we get, k = 2.   Now the equation (as k = 2) become, S = 24-2√n;   Thus, it means when n = 144, speed will be zero. Hence, train can just move when 143 wagons are attached.   Answer: Option 143
<result>C</result>
The Lucknow-Indore Express without its rake can go 24 km an hour, and the speed is diminished by a quantity that varies as the square root of the number of wagon attached. If it is known that with four wagons its speed is 20 km/h, the greatest number of wagons with which the engine can just move is