Tushar a motorist uses 24% of his fuel in covering the first 20% of his total journey (in city driving conditions). If he knows that he has to cover another 25% of his total journey in city driving conditions, what should be the minimum percentage increase in the fuel efficiency for non-city driving over the city driving fuel efficiency, so that he is just able to cover his entire journey without having to refuel? (Approximately)

Question

anonymous · Answer

This is pretty difficult for me, I will give it a go though:

The method that I would use is ratios.
We can say that 24% of fuel is equivalent to 20% of driving:
Therefore: 24:20
and there is 45% of city driving in total so alter the ratio accordingly:
24:20
54:45    (multiply both sides by 2.25)

Therefore he will use 54% of his fuel after 45% of the journey.
By using this we can say that he has 46% of his fuel left for 55% of his journey.

Fuel efficiency is generally measured in distance traveled divided by the amount of fuel used. We can use this to calculate the efficiency for the city driving: 45%/54% = 0.833% of distance per 1% of fuel.

In order for the journey to be possible, he must use the amount of fuel left to travel the distance left so: 55%/46% = 1.196% of distance per 1% of fuel

We can now compare the two efficiencies. The question asks for non-city over city so: 1.196/0.833 = 1.436 which is 144% in a percentage.

So the increase in efficiency would have to be 144%.

anonymous · Answer

43.6 efficiency.becoz 100-143.6=43.6%

anonymous · Answer

Yeah, there are a few ways of expressing it. I just like leaving that 100% on there because it's correct in a fractional sense.