Why Might a Math Solution Involve Doubling the Percentage Difference?

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SUMMARY

The discussion centers on the calculation of percentage difference in a math problem involving vertical height gained, specifically comparing 1.355 m to a baseline of 1.1 m. The original poster calculated a percentage difference of 11.48% using 1.2 m as the baseline, while the mark scheme indicated a percentage difference of 23% using 1.1 m. Participants clarified that the correct approach is to use 1.1 m as the baseline for comparison, leading to a revised calculation of the percentage difference.

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tahmidbro
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Homework Statement
My answer does not match with the ones in book
Relevant Equations
N/A

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If you read the question, you will find that you were asked to compare against 1.1, not against 1.2
the poorly quoted question said:
Compare your answer with the 1.1 m calculated in the...
 
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tahmidbro said:
Homework Statement:: My answer does not match with the ones in book
Relevant Equations:: N/A

See the question : https://www.thestudentroom.co.uk/att...hmentid=978958

The mark scheme/answer : https://www.thestudentroom.co.uk/att...hmentid=978956

I have got the answer to the vertical height gained = 1.355 m. No problem.

But not the value of the percentage difference. Their value : 23%, my value =( (1.355-1.2 )/1.35) x 100% = 11.48%

Well, I suspect that they are multiplying %D by 2, but why?
Your first link says the calculated height is 1.1m, not 1.2m.
You are asked for the % difference relative to 1.1m, so you should divide (1.355 - 1.1) by 1.1
 
Now I understand. Thank you!
 
I have a minor quibble with the response given by @Steve4Physics. He points out quite correctly that if one is computing the percentage difference of 1.355 from 1.1 that one should divide the delta by 1.1.

However, the question at hand does not specify whether we should use the 1.1 or the 1.355 as the baseline.

the poorly quoted question said:
calculate the percentage difference between the two answers
There is nothing in that request that elevates either of the two answers to the status of baseline. One could argue for the correctness of any of three possible answers to this ambiguous question.

1. ##\frac{\text{high}-\text{low}}{\text{low}}##
2. ##\frac{\text{low}-\text{high}}{\text{high}}##
3. ##\frac{\text{high}-\text{low}}{\text{high}}##
 
Sorry for forgetting to upload the 'worked example' along with the question
My bad :-d
 

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jbriggs444 said:
There is nothing in that request that elevates either of the two answers to the status of baseline. One could argue for the correctness of any of three possible answers to this ambiguous question.
Agreed that the question isn't particularly well expressed, but the OP's first link explicitly says
"Compare your answer with the 1.1m calculated in the worked example..."
which implies 1.1m is the 'baseline'.
 
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tahmidbro said:
Sorry for forgetting to upload the 'worked example' along with the question
My bad :-d
For future reference, it is much easier to quote sections of the problem if it is transcribed as text rather than attached as an image.
 
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