Percentage problem

Mar 2015

I am currently working through Geoff Renshaw Maths for Economics book and I am quite puzzled by this one percentage problem that I am suppose to solve.

Here is the problem: ( Car A uses 10 litres of fuel and car B uses 5 litres of fuel, for every 100km travelled. By what percentage does car A's fuel consumption exceed car B's ? What will be the percentage reduction in fuel used if I switch from car A to car B ? Why are the two answers different ? )

Here is my answer so far: Car A exceeds car B's fuel consumption by 100%... but here is what I get but am not sure, in my opinion the reduction is 50% if I switch from car A to B. is this right?, any help would be very much appreciated.

Thanks in advance
Last edited:


MHF Helper
Jun 2008
North Texas
percentages always confuse people because they either never learn (or forget) that a percentage is a comparison between two values

Car A uses 5 more liters of fuel as the 5 liters used by car B ... the comparison is 5 more to 5, or 100%

Car B uses 5 less liters of fuel as the 10 liters used by car A ... the comparison is 5 less to 10, or 50%
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