I'm having trouble understanding significant figures. If a problem is requires two equations to finish, which of the original measurements do I use to figure out the significant figure? For ex. 3.001+4.32= 7.321. Then I use this answer for a different equation..for the final answer do I use the measurements for the second eq. or the first measurements?
Both. Determine the number of s.f. for the first operation, then go to the second and determine the number in the final answer. Use 7.32 for the correct number from the first operation.
Here is a good site you can use.
http://www.chemteam.info/SigFigs/SigFigs.html
When dealing with significant figures, there are certain rules to follow. In your example, the number 3.001 has four significant figures, while the number 4.32 has three significant figures.
When adding or subtracting numbers, the rule is to round the result to the least number of decimal places of any number in the calculation. In this case, the number 4.32 has two decimal places, so the final result should have two decimal places as well. Therefore, the result of 7.321 should be rounded to 7.32.
Now, when using this result in a subsequent equation, you should use the rounded answer of 7.32. The reason for this is that the significant figures of the final answer are determined by the least precise value in the calculation, which was the rounded answer of the addition. So, regardless of the measurements used in the second equation, stick with the rounded answer obtained from the previous calculation.
Remember, significant figures are used to reflect the precision of a measurement, so it's important to be consistent and use the correct number of significant figures throughout the calculation.