Chemistry- urgent!

Perform the following operations and express the results in the correct number of significant digits or decimal places. Express all results in scientific notation. Please help me I'm so confused on how to do this!!

15. (1.71 x 10^6)(6.73 x 10^-8)/2.25 x 10

20. (533)(24)

21. (1.55 x 10^6)(3.05 x 10^-8)^2/(6.53 x 10^-9)^3

22. �ã9.74 x 10-3 + 9.65 x 10-4

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  1. You need to know the rules for significant figures. Here is a good site. Study it carefully.
    http://www.chemteam.info/SigFigs/SigFigs.html

    For 15: All multiplication and division. The s.f. rule is the final answer can have as many s.f. as the LOWEST number involved. All of them are 3 s.f.; therefore, you can have 3 s.f. in the answer. I didn't run the number because I think you omitted a number on the exponent of 10.
    For #20. All multiplication so you can have 2 s.f. as dictated by the 24. My calculator gives 1.2792E4 so this is rounded to 1.3E4.
    For 22:
    In addition and subtraction you are allowed the minimum number after the decimal point, (I don't now what the a squigly line is. I'll assume that is not supposed to be there.
    0.00974
    +0.000965
    ---------------
    0.010705
    The first value is the least precise so you can use anything past 0.00001. So we round the final answer to
    0.01070 (and I'm using the rounding rule that says round a 5 to the nearest even number).

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    posted by DrBob222

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