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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: 21385 on March 09, 2008, 11:21:19 PM

Title: rounding question
Post by: 21385 on March 09, 2008, 11:21:19 PM

for a question with multiple calculations, do you round at the end, or at every step? As in if I got 47690 for the first step in the calculation, do I use 47690 or a rounded number such as 48000 in the next calculation?

thanks

Title: Re: rounding question
Post by: Yggdrasil on March 09, 2008, 11:25:19 PM

You should round only at the end.

Title: Re: rounding question
Post by: 21385 on March 09, 2008, 11:42:29 PM

Thank you

I have another concern.

If a hypothetical question requires this kind of equation X=(34.54*45.4) + (45.34*54.334) + 30002, should u round after you multiply the contents of the brackets, or can you assume that they are separate calculations and round only at the end?

This is because the result would be different.
Situation 1 (round after multiplying the contents of the brackets)
X=1570 + 2464 + 30002
 = 34036
Situation 2 (rounding everything only at the end, imagine the brackets are separate calculations)
X=1568.116 + 2463.5 + 30002
  =34034 (rounding only at the last step)

Thanks

Title: Re: rounding question
Post by: Yggdrasil on March 10, 2008, 12:33:21 AM

You should round only at the last step.  However, it should be noted that the answer will have only 4 significant figures and the two values are the same to 4 sig figs (since the last sig fig can vary).