How do i work out significant figures?

4.67 52.4 797 3470 0.00368 would be examples of numbers to three significant figures.

The question i am being asked is 7.21 divided by 8.3-2.76

the answer i get from that i need to change to 3 significant figures

Assuming the 8.3-2.76 are in brackets, my calculator gives the answer as 1.3014440433212996389891696... actually it goes on for quite a bit but I got bored. How significant are the numbers on the (right hand) end anyway? Your task is not to change anything much but just to express the number to a "near enough" figure. The only real decision you have to make is which number is closer to the "true" value, 1.30 or 1.31?

a significant figure is as ian has said... always remember significant means the most important number(s)

Hi, just to remind you that the answer can only be as accurate as the least number of significant figures suggested by the question. So if you have figures of 7.,21, 8.3 and 2.76. You answer can only be accurate to 2 significant figures at best. So answer is 1.3

General rules on significant figures:

Rule 1: Significant figures tell you how precise your number is, e.g. 1.12 cm means you are precise to the nearest one hundredth of a cm (nearest 0.01 of a cm). This means that you need to be quite careful when you start working with more complicated numbers involving decimal places and zeros. Rule 2: Numbers which are not zero or 'sandwiched' zeros need to be counted so "104" has 3 sig fig, "1967" has 4 sig fig "4.5" has 2 sig fig. Rule 3: To get to your last number you round the following number up or down depending on whether it is less than 5. You don't go down the line. So, 13.349 to three sig fig is 13.3 because 4 is less than 5. Ignore the 9. Rule 4: If your number is less than 1 then the zeros before and straight after the decimal point are not significant e.g. 0.00123 has 3 sig fig which are 1,2 and 3. But, any following zeros are, so 0.001230 has 4 sig fig. The final zeros is telling you that you were precise to this fraction (a millionth in this case) Rule5 : Trailing zeros can be ambiguous. "2000" could be either 1 sig fig ("2") or 4 sig fig ("2000"). Rule 6: If you have something like 12.0 the final zero is significant because it is telling you you have no tenths. So, 2000.00 has 6 sig fig. Phew. If you are still unsure Google 'significant figure calculator' and you will find sites where you can type in your number and it will tell you - try out some awkward ones - you'll soon get the hang of it.