Rounding off answers -- whats the rule? (1 Viewer)

[mAtboisLim]

If there was a multi-section calculation question, for example:

Question 1
(a) Calculate.....
(b) Calculate....

And the answer to part (a) had to be substituted into part (b) --- can you use the rounded off (to as many significant figures as the least accurate input) answer you wrote in part (a), or must you use the full calculator display value for the calculation in part (a)?

In other words, do you only round off for the final part of a multi-section calculate question?

 

[Emma-Jayde]

I've always been taught to round off at the very end. Which makes sense because if you have to do a couple of calculations amd you used rounded answers, they don't really end up being close to the answer you should get.

 

[zenger69]

I'd say in Physics round to 3 decimals places when substituting into (b). And if the question doesn't specify how many decimal places, I round it off to 2 decimal places.

My teacher also says the answer isn't very important, even if you get the answer wrong she still gives you full marks for correct usage of the formula.

But in maths i'd use the full 8 decimal places and use that STO --> 2NDF --> A
like A to F storage function. Or leave it in exact form.

 

[Trebla]

I'm one of those people who like exact values. When it comes to physics calculations, I tend to leave answers as a fraction or surd unless rounding off is indicated and required in the question. I often ended up with fractions that contained large numbers in the numerator and denominator. My teacher wasn't happy with that though...

 

[Xayma]

I'm one of those people who like exact values. When it comes to physics calculations, I tend to leave answers as a fraction or surd unless rounding off is indicated and required in the question. I often ended up with fractions that contained large numbers in the numerator and denominator. My teacher wasn't happy with that though...

The problem here begins when you start using experimental values for constants (eg gravity is not 9.81ms^-1 exactly, so you shouldnt have more then 3 sig figures in your answer if it contains it).

If you have two parts a) and b) you should round off your answer for a) and write it down, but use the full calculated value for b).

 

[munkaii]

My general rule of thumb is that i express my answer in 2dp if it doesnt specify exact value. But if there are more sections to the question, ill use the exact value expression (usually stored in calc) to answer the following questions.

 

[Jumbo Cactuar]

For chemistry it is as many significant figures as the least amount of significant figures in the data given.

Never round off during a calculation and underline all your final answers (which will be in appropriate sig figs).

 

[Jumbo Cactuar]

Also consider that much of physics is a model of the real world, and not a perfect model. Mathematicians desire for exactness caused engineers and theoreticians to not see eye-to-eye for centuries.

What I am trying to say is physics calculations are never a true relation and therefore exactness has no use. It is easier to make comparisons if your answer is enumerated.

Pure mathematics is a different kettle of fish.

 

[DAAVE]

Technically your answer to part A is only accurate to the least number of significant figures they give you in the data. So say if they gave you g = 9.81 and this was the number with the least sig figs, it would be all you could give your answer to (ie 3 sig fig). You would then use this answer in your next part, because it's somewhat meaningless to get, for example, an irrational answer and sub it into then next part...

 

[angelduck]

Yep, round off numbers in relation to data given, but use full unrounded version in 2nd part, otherwise your answer could be wrong, and dont be fooled, you get marks for the CORRECT answer, not just your use of the formula

 

[Jumbo Cactuar]

"CORRECT" by the marker's definition