1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Significant figures with multiplication

  1. May 27, 2013 #1
    1. The problem statement, all variables and given/known data

    what is 33.3 X 45.1 using significant figures?


    2. Relevant equations

    basic multiplication and significant figures.

    3. The attempt at a solution

    I got 1501.83 in my calculator. I'm confused with the original problem because it has 4 digits before the period however you have to round the answer to 3 significant figures. (It isn't asking for scientific notation)

    is it any of these: ≈1501 or ≈1502 or ≈1500?
     
    Last edited: May 27, 2013
  2. jcsd
  3. May 27, 2013 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    note ##0.33\times 10^2 = 3.33\times 10^1 =33.3 = 333 \times 10^{-1}## all have 3 sig fig.
    so... ##1502=1.502\times 10^3## how many sig fig?
     
  4. May 27, 2013 #3
    1.502X10^3 has 4 significant figures.

    Hmm I thought 0.33 X 10^2 has only 2. Why does it have 3 significant figures?

    Anyway I'm confused with the original problem because it has 4 digits before the period (1501.) however you have to round the answer to 3 significant figures. Its not asking for scientific notation.
     
    Last edited: May 27, 2013
  5. May 27, 2013 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Argh - because it's a typo.

    But putting things in scientific notation can be a way to check you have the right sig fig.

    Scientifically, 3.33 and 3.30 have the same sig fig ... but you cannot tell of 330 is 2 or 3 sig fig.
    (a measurement of 3.3 units is different from a measurement of 3.30 units)

    Your problem is that you cannot see if "1500" is 2, 3 or 4 sig fig.
    But if you wrote 1.50x103 it would be clearer right?

    Also - consider 0.02 ... how many sig fig? That's 2x10-2 ... that help?
    What if it was the result of 66/3300 ?

    The bottom line is that the sig-fig approach is not all that useful.
    You will stop using it when you leave secondary school.

    The correct way to write that result is: 1500 units (3 sig-fig)
     
  6. May 28, 2013 #5
    i see. thankyou
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Significant figures with multiplication
  1. Significant figures (Replies: 1)

  2. Significant figures (Replies: 13)

  3. Significant figures. (Replies: 5)

  4. Significant figures (Replies: 6)

Loading...