9514 1404 393
Answer:
8.83 × 10⁻³
Step-by-step explanation:
Your calculator can do this for you. Your scientific or graphing calculator can be set to display the answer in scientific notation, if you need that. Any spreadsheet can do this, too.
The formula for a spreadsheet would be =8.65e-3+2.7e-4-9e-5.
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If you want to do it "by hand", you can factor out 10⁻³ to get ...
8.65×10⁻³ +2.7×10⁻⁴ -9×10⁻⁵ = (8.65 +0.27 -0.09)×10⁻³ = 8.83×10⁻³
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Additional comment
Since the values after the first have more negative exponents, those numbers will affect digits farther right than the decimal point in the first number. (You can see this in the sum shown above.) Simply by estimating, you can determine that the answer will be slightly more than 8.6×10⁻³, but not as much as 9.01×10⁻³.
