# Significant figures/rounding what the heck.

1. Dec 16, 2006

### dontdisturbmycircles

Didn't use the template because it didn't make sense to do so for my question..

Simple question here regarding significant figures. I am working through a textbook and in the answer section they often seem to round off to odd numbers which makes no sense to me. I decided to ignore it at first because I am so sure that I am doing it correctly, I mean... I learned to round in grade 2 . But it seems to happen a lot and I figure that the person writing the text wasn't an idiot so...

for $$\frac{1.20kg}{2.99x10^{-26}kg}$$ they have their answer as $$4.02x10^{25}$$. I say that its $$4.01x10^{25}$$

Who's right? and why if I am not right.

Last edited: Dec 16, 2006
2. Dec 16, 2006

According to my TI-83, you're right. Why is this bugging you? It's irrelevant. They often make mistakes, since writing down solutions on back pages of books isn't a very exciting and caution-keeping job.

3. Dec 16, 2006

### dontdisturbmycircles

Okay, I thought I was losing my mind or something. lol

Last edited: Dec 16, 2006
4. Dec 16, 2006

### dontdisturbmycircles

I definitely agree that it is pretty insignificant, but it was happening like 1/5th of the time so it started to bug me.

5. Dec 16, 2006

### Hurkyl

Staff Emeritus
You have to remember that significant figures are a heuristic device that usually approximates a reasonable estimate of error.

As such, there really isn't a "right" answer, and there are several different approaches to it. For example, "round to the nearest even number" is not terribly infrequent.

6. Dec 16, 2006

### carbz

Yes. Just remember that with rounding to Sig. Figs, that as long as your answer is realitively close to the correct answer, it's correct. I mean, most times you wouldn't get the same answer, but just make sure yours is around it.

7. Dec 16, 2006

### dontdisturbmycircles

Alright great. Thanks :)