Math CentralQuandaries & Queries


Question from Brian:

we had a 2.43% scrap rate last year, compared to a 1.28% this year. does this come out to a .47% improvement?
Thanks for your help

Hi Brian,

1.28 is approximately half of 2.43 so the scrap rate has been cut nearly in half. If you want to say it in percentage terms the calculation is

[(new rate - old rate)/old rate] × 100 = [(1.28 - 2.43)/2.43] × 100 = - 47%

I would however not say there is a 47% improvement as this might be interpreted as the amount of scrap has been reduced by 47%. It is always dangerous to calculate with percentages. The numbers 2.43% and 1.28% are percentages of different things. You need to be careful to report that it is the RATE which has been cut in half.


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