Algebra
Aptitude

 Back to Questions

Common Information

The cost of fuel for running the engine of an army tank is proportional to the square of the speed and Rs. 64/hour for a speed of 16 kmph. Other costs amount to Rs. 400/hour. The tank has to make a journey of 400 km at a constant speed.

Q.

Common Information Question: 2/2

The total cost for the journey at this most economical speed is:

 A.

Rs 6,000

 B.

Rs 8,000

 C.

Rs 10,000

 D.

Rs 11,000

 Hide Ans

Solution:
Option(B) is correct

Cost of fuel is proportional to square of the speed:

\(E=KS^2\)

\(\Rightarrow E=64 \text{ and } S=16 \)

\(K=\dfrac{1}{4}\)

Total cost 

\(=\dfrac{1}{4}\times S^2t+400t\)

Most economical speed, checking options we get most economical speed at 40km/hr.

Total cost at 40km/hr

\(=\dfrac{1}{4}\times 40^2+400\left(\dfrac{400}{40}\right)\)

\(=\text{Rs }8,000\)


(2) Comment(s)


Siddhi Verma
 ()

It should be 400+4000=4400



Bhumit
 ()

It should be 4000 + 400 = 4400 !!