Typo in Cracking the AP Chemistry Book?

Test Preparation AP Test Preparation
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<p>When they introduced significant figures addition/subtraction, their example is:</p>

<p>780 + 35 + 4 = 819</p>

<p>Perhaps they forgot a period after the 780? Because that is blatantly wrong. The answer should be 820 since the least significant position is the tens place.</p>

<p>The book says that only decimal is counted in analysing the sig figs, but this is wrong as well:</p>

<p>For example, 500 + 21 = 5 x 10^2 + .21 x 10^2 = (5+.21) x 10^2 = 500</p>

<p>You can generalize looking at decimals to integers. Thus the addition/subtraction rule applies to all positions of a number, not just the decimal portion. This is also the way we do it in all of the science classes I have taken.</p>

<p>Who agrees?</p>

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<p>the way that they have it in the book is correct. when you're adding/subtracting significant figures you only take into account the amount of significant figures after the decimal and round it to the least amount. therefore 780+35+4=819. in your other example with the 500+21 those indeed yield different results 500+21=521 and 5x10^2+.21x10^2=5x10^2. putting it into scientific notation makes it a different kind of estimation. although this is just about the least "significant" topic that you have to know if you still have questions refer here: <a href="http://en.wikipedia.org/wiki/Significance_arithmetic%5B/url%5D"&gt;http://en.wikipedia.org/wiki/Significance_arithmetic&lt;/a&gt;&lt;/p>

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<p>dashms is right.</p>

<p>If you're going to put it into scientific notation, then you have to be more exact as to the number of sig figs. In other words, is it 500 or is it 500.? If it is the latter, then in scientific notation you would write 5.00 x 10^2.</p>

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<p>So when do you use the two different methods?</p>

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<p>however if you go to page 198, there is a typo. The first order rate law should have a suptraction sign between the two ln's</p>

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<p>Ah yes I noticed this.</p>

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<p>yeah i was doing some classwork and used the formulas in the book and got stuck.. then my teacher told me that there was a typo lol</p>

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<p>I know this is an older thread, and sig figs aren't all that important, but I can't leave a mistake uncorrected. Dashms308's explanation is not correct, il bandito's interpretation is. Using sig fig rules, 500 + 21 = 500. It is <em>not</em> correct to assume that the trailing zereos are signficant and arbitrarily rewrite this as 5.00x10^2. At best, the trailing zeroes are ambiguous, and most sources (ex: Zumdahl) teach that trailing zeroes are assumed to be not significant unless there is decimal. It doesn't matter whether the trailing zeroes are ones, tens, hundreds, etc, or whether they are tenths, hundredths, thousandths etc.
The AP test will <em>always</em> write the number as 500. if they intend the zeroes to be significant.</p>

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<p>Thank you gfaith!</p>