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General Rules of Approximation While Solving Problems

U

usmankhaliq

Member
Hey everyone. I need to ask you guys a pretty basic stuff. While solving a few past paper questions, I noticed that my answers were a few decimal places off from the ones given in the examiner report. I realised that this discrepency was there because I was plugging in the entire formula in my calculator, storing the intermediate values with all the decimal places and then using them to find my answer, whereas in the solutions provided in the examination report, the intermediate values had been taken upto a certain decimal place, hence leading to the irregularity in the answers. I have a couple of things to clarify regarding this:
1) Is the method which I am using the correct one, i.e. storing the exact intermediate values in the calculator and then using it, or am I supposed to choose the values upto a certain number of significant figures/decimal places?
2) Should there be any discrepency between my answers and the ones given in the examinations if our methods are slightly different?
I would be extremely grateful if someone could help me out with this. Cheers :)
 
If this is the only issue it won't affect your marks.

But when you say store results, do you write down any intermediate values?
Sometimes if you write down say the value of an annuity and you go wrong somewhere else you will pick up some marks.

If you only give the end result, then mathod marks are hard to get.

Remember too that you don't always need to evaluate something from scratch. Check whats in the tables and use these values - can save you making an arithmetic slip.

Hope this helps
 
Hey Bystander. Yeah even I thought that the safer way would be to write the intermediate values too instead of just showing the final answer. Thanks:)
 
I concur. Storing on your calculator will be much faster than retying in rounded numbers.

But writing down your calculations allows the examiners to award you method marks - otherwise you're playing exam roulette with your marks (ie all or nothing).

When I attend the examiners meeting I ensure that accurate answers as well as those using the rounded values from the Tables are awarded full marks.
 
Thanks John Lee. One more thing: if I am rounding the values from the calculator, till how many significant figures/decimal should I round up the intermediate values to? Cheers.
 
usmankhaliq said:
Thanks John Lee. One more thing: if I am rounding the values from the calculator, till how many significant figures/decimal should I round up the intermediate values to? Cheers.
Click to expand...

Well the easiest way is to write something like:

1.82567....

to indicate you've kept the whole number but just aren't writing it all down.

Then you can give your answer to 3 SF (for percentages or probabilities), 5 SF (or nearest pound or penny).

However if you do choose to round intermediate answers (but keep the full answer on your calculator) then perhaps you should tell the examiners that's what you're doing at the start of the paper - so when they look for follow through marks you do get them.
 
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