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I have a homework problem that is asking me for something. Here's the last line quoted:

If you switch to the ring, by what part will you decrease the electric field magnitude at P?

Okay, so the only problem that I'm facing is that I'm not sure whether this wants a percentage, or a decimal. For example, my answer came out to be 0.11. Would this be asking for 11%, or just the decimal like it is right now?

Thanks, and sorry for such a basic question.

Edit: the whole question reads like the following:

Suppose you design an apparatus in which a uniformly charged disk of radius R is to produce an electric field. The field magnitude is most important along the central perpendicular axis of the disk, at a point P at distance 3.10R from the disk (Fig. 22-52a). Cost analysis suggests that you switch to a ring of the same outer radius R but with inner radius R/3.10 (Fig. 22-52b). Assume that the ring will have the same surface charge density as the original disk. If you switch to the ring, by what part will you decrease the electric field magnitude at P?

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Perhaps you should add the rest of the question, just like that, nothing is obvious. – Patrick Da Silva Mar 31 '12 at 20:13
@PatrickDaSilva: I added it for you. – BigBoy. Mar 31 '12 at 20:14
Personally, I'd ask the instructor, but if this is not an option, I'd just write both. E.g. [..] by 0.11, i.e. 11%. – user2468 Mar 31 '12 at 20:22
@J.D.: How I wish I could do that. Unfortunately, the grading system is computerized, so the answer is either right or wrong, no explanations accepted. – BigBoy. Mar 31 '12 at 20:23
Ops! Good luck then! – user2468 Mar 31 '12 at 20:25
up vote 0 down vote accepted

The question suggests that "by what part" means "by what percentage". But then again, context makes this more easy to guess. I would go with the percentage.

Hope that helps,

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I sure do hope you're right. I only have once chance at getting this problem correct. If it's wrong, I'm going to come back here and blame you for all my troubles. Deal? Just kidding. ;) – BigBoy. Mar 31 '12 at 20:20
I am not saying that I am right, because I have no means of confirmation :P I'm just saying what I think feels right with what I see. – Patrick Da Silva Mar 31 '12 at 20:21
I doubt they're going to knock you a mark for putting the percentage if they wanted it in some other form. You got the right value - I assume - so it shouldn't matter what form you put it in. – Donkey_2009 Mar 31 '12 at 20:23
Ops! Good luck then! – Donkey_2009 Mar 31 '12 at 20:26
Yep, just got it wrong. It ended up being a decimal like my original answer was. Hopefully I can contact my instructor and show him what I entered. Accepted for your troubles. – BigBoy. Mar 31 '12 at 20:27

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