# Moderate Algebra Solved QuestionAptitude Discussion

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: 1/2 The most economical speed for this January is:
 ✖ A. 10 kmph ✖ B. 20 kmph ✖ C. 35 kmph ✔ D. 40 kmph

Solution:
Option(D) 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.

Edit: A typo has been corrected in the question after it has been pointed out by Sai Rajesh.

## (2) Comment(s)

Sai Rajesh
()

Please correct "Rs. 64 hour" to Rs. 64 per hour or Rs. 64 / hour & similarly "Rs. 400 hour" to Rs. 400 per hour or Rs. 400 / hour.

Deepak
()

Thank you Sai Rajesh for pointing it out, corrected the typo.

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