[splinter]

Hi, I am taking a practice test and I have no idea why it came to be this answer can someone explain it to me.

How many significant figures should be reported for the difference between 235.7631 and 235.57?

The answer was 2. Why is that, I would expect it to have at least 5 sig figs.

--------------------------------------------

Three different samples were weighed using a different type of balance for each sample.
The three were found to weigh 0.1568934 kg, 1.215 mg, and 2458.1 g. The total mass of
the samples should be reported as
a. 2614.994615 g.   b. 2614.9946 g.   c. 2614.995
d. 2615.0  g.   e. 2615 g.

With this problem Do I just add all of the samples? if so, I added them up and it gives me a total of 2459.471. The answer is D

----------------------------------------------

The age of a wooden artifact was determined by carbon-14 dating. Three different
measurements gave values of 6295, 4815, and 5485 years. Its age would best be
reported as
a. 5531.7 years. b. 5532 years. c. 5530 years.
d. 5500 years. e. 5000 years.

On this one, do I just add all the values and take the average?  And the answer for this one is E

How?

[Donaldson Tan]

I agree with you with regards to Q(1). The answer is 2 decimal points.

Q(2) involves addition. Since the smallest decimal point among the quantities is 1, then the average weight should be quoted in 1 decimal point.

Q(3) involves addition again.  Since all quantities are expressed in 4 significant figures, then the answer would be (b).

[Lexus74]

For question one, since it is just subraction (same for addition), you have to round to the least number of decimal points.

For multiplication, round to least sig figs.

[goddessxx]

If the test allows it, you should bring along Graphic Calculator.  All the TI brand has the SigFig calculator built into it.