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
A. 144
B. 140
C. 143
D. 124
E. 142
Answer: Option C
Solution(By Examveda Team)
Speed = $$24 - {\text{k}}\sqrt {\text{n}} $$ Putting the value, n = 4 we get, k = 2 Now the equation (as k = 2) become, S = $$24 - {\text{k}}\sqrt {\text{n}} $$ Thus, it means when n = 144, speed will be zero.Hence, train can just move when 143 wagons are attached
This Question Belongs to Arithmetic Ability >> Ratio
Join The Discussion
Comments ( 3 )
Related Questions on Ratio
If a : b : c = 3 : 4 : 7, then the ratio (a + b + c) : c is equal to
A. 2 : 1
B. 14 : 3
C. 7 : 2
D. 1 : 2
If $$\frac{2}{3}$$ of A=75% of B = 0.6 of C, then A : B : C is
A. 2 : 3 : 3
B. 3 : 4 : 5
C. 4 : 5 : 6
D. 9 : 8 : 10
let, x=24 kmph
y=20 kmph
N=(x^2/x-y)-1
=143
Speed = $45 - k sqrt{n}$ where n is the number of wagons
Speed with 9 wagons = $45 - k sqrt{9}$
$45 - k sqrt{9}$ = 30
45 - 3k = 30
3k = 15
k = 5
i.e., speed = $45 - 5 sqrt{n}$
Consider the case when the speed is zero
$45 - 5 sqrt{n} = 0$
$ 5 sqrt{n}= 45$
$ sqrt{n}= 9$
n = 81
This means, when the number of wagons = 81, speed = 0
i.e., when the number of wagons = 80, the train can just move
another way to solve the problem please