significant figures

[syed786]

evaluate the following expressions and express the answer with the appropriate number of significant figures.

A) 320.55-(6104.5/2.3)
B.)[(285.3 x 10^5)-(1.200 x 10^-3)] x 2.8954
C.) (0.0045 x 20 000.0)+(2813 x 12)
D.) 863 x [1255-(3.45 x 108)]


im not sure if my answers are right, i got: a) -2333.55
b.) 82605762= 8260
c.)33846=3385
d.) 761511.2= 761

PLEASSSSE help me as soon as possible!!!!!!!

[RobJim]

A)

320.55 - (6104.5/2.3)
320.55 - 2700
- (2700 - 320.55)
- 2400

Your answer doesn't take into account the SF I believe. SF are confusing though.

B)

[(285.3 x 10^5)-(1.200 x 10^-3)] x 2.8954
(28530000 - 0.001200) x 2.8954
28530000 x 2.8954
2.853 x 10^7 x 2.8954
8.261 x 10^7
2.861

C)

(0.0045 x 20 000.0)+(2813 x 12)
(4.5 x 10^-3 x 2.00000 x 10^4) + (3.4 x 10^4)
9.0 x 10^1 + 3.4 x 10^4
90 + 3400
3490

D)

863 x [1255-(3.45 x 108)]
863 x [1255 - 372]
863 x 883
7.62 x 10^5

[Jim Wales]

Originally Posted by RobJim

A)

320.55 - (6104.5/2.3)
320.55 - 2700
- (2700 - 320.55)
- 2400

Your answer doesn't take into account the SF I believe. SF are confusing though.

Standard practice is not to round until the very end of the calculation.

320.55 - (6104.5/2.3)

Put these numbers into your calculator to get

= -2333.580435

Then note that in your division you used a number with only 2 SF. So you round your answer to 2 SF.

= -2300