Ask Me Help Desk

Ask Me Help Desk (https://www.askmehelpdesk.com/forum.php)
-   Chemistry (https://www.askmehelpdesk.com/forumdisplay.php?f=68)
-   -   Not sure how they got theses answers. (https://www.askmehelpdesk.com/showthread.php?t=18874)

  • Jan 26, 2006, 03:50 PM
    killasnake
    Not sure how they got theses answers.
    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

    can someone explain how they got the answers?
  • Jan 26, 2006, 04:03 PM
    CaptainForest
    Problem 1: I agree with you. I would have thought 5 sig figs as well.


    Problem 2: The answer is D.

    You can't just add them all up since they are all different units.

    The Answer is D: 2615.0 g

    0.1568934 kg = 156.8934 grams
    1.21500 mg = 0.001215 grams
    2458.1 g = 2458.1 grams

    Total = 2614.995 grams

    The answer is D though, not C because you have to account for significant digits (figures)
  • Jan 26, 2006, 04:23 PM
    killasnake
    Quote:

    Originally Posted by CaptainForest
    Problem 1: I agree with you. I would have thought 5 sig figs as well.

    I know, I just don't know where they came up with just 2 sig figs
    Quote:

    Originally Posted by CaptainForest
    Problem 2: The answer is D.

    You can't just add them all up since they are all different units.

    The Answer is D: 2615.0 g

    0.1568934 kg = 156.8934 grams
    1.21500 mg = 0.001215 grams
    2458.1 g = 2458.1 grams

    Total = 2614.995 grams

    The answer is D though, not C b/c you have to account for significant digits (figures)

    Ah... I see thank you... ** "duh" to myself **:D
  • Jan 26, 2006, 06:03 PM
    killasnake
    I find out why the first question has 2 sig figs

    235.7621
    -235.57
    ________
    000.39.?

    And there are 2 :)

  • All times are GMT -7. The time now is 02:27 AM.