<p>Sorry this has not much to do with the SAT subject test but:</p>
<p>At my school some people in grade 12 started a group thing called 'SACS' which stands for 'Socety Against Chiffres Signicatif' (AKA in english: SASF Society Against Significant Figures) and I was just curious about what a significant figure actually is. </p>
<p>Thanks.</p>
<p>Particularly in chemistry calculations it is believed that if a certain number is only so accurate, then any calculation derived by that number can only be as accurate. For example, if you multiply something with three significant figures by something with six, then the answer must be rounded to three significant figures because that's how accurate the first allows it to be. How do you determine what figures in a number are significant? Here are general rules. Significant figures will be in bold.</p>
<ol>
<li> Leading zeroes a not significant</li>
</ol>
<p>00.00*82, .0024*</p>
<ol>
<li> Zeros between two non-zero numbers are significant.</li>
</ol>
<p>8005, 21,031</p>
<ol>
<li> Zeros behind the decimal that are not leading zeros are significant.</li>
</ol>
<p>54.00, 1.000000000, 00*8.010000*</p>
<ol>
<li> All constants are significant.</li>
</ol>
<p>00*589.8783*</p>
<p>When adding numbers, you can have as many significant digits as you want total to the left of the decimal, but only the limiting number to the right. For example, if you add 4.31 and 5.2, the answer must be rounded to 1 spot behind the decimal. Same with subtraction.</p>
<p>When multiplying, you must round the the lowest number. For example, 340 mutliplied by 32 must be rounded to only two digits. Since the answer is more than two digits, use scientific notation. The same goes with dividing.</p>
<p>When calculating pH, the numbers behind the decimal can go as far as the total numbers in the [H+], and the numbers behind the decimal in a pH determine how many numbers can be used when calculating the [H+]. The same with pOH. Example: If pH = 1.00, then [H+] = 1.0 x 10 ^ -1</p>
<p>Never round before the final answer, don't round significant digits in the middle of a single calculation. Round when one particular value is found. If using one value to find another value, then round the first value to proper significant digits after all of the calculations. </p>
<p>Exact numbers have infinite significant digits. For example, my brother and I are exactly two people. Therefore, if I considered us '2', that would be infinite significant digits, not one. Things that do have significant digits are things like measurements of length. If I say something is 1 inch, that's to one significant digit. Exactly 12 inches, however, make up 1 foot, so you don't have to use significant digits when converting between units of a similar system--for example, from meters to kilometers, 1 km = 1000 m, not 1 x 10^3 km. </p>
<p>I hope this answered your question.</p>
<p>this would have helped me with my chem test in september!</p>
<p>Also keep in mind that 1 in is exactly equal to 2.54 cm. Even though you are switching systems, there is no loss of significant digits.</p>
<p>but if you used the 1 in or 3 feet or whatever.... those digits don't count right? for instance... when you divide... 5.4/3 ft... then it would be 2 sig fig... since 3 doesn't count</p>
<p>The information you gave is incomplete, so it's hard to say. If you're taking something 5.4 feet long and something 3 feet long and finding their ratio, the answer would be 2. If you've got 5.4 feet and you're converting to yards, then it would be 1.8 yards.</p>