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Re: [mathlearn] significant digits
Posted:
Feb 28, 2002 1:31 PM


Well, I guess I can't get away without continuing with how I solved this problem. :) I didn't convert the meters/second to miles/hour. Instead I stopped at that point that I had a list of all of the speeds using either 4 or 5 significant digits and I changed the 25 miles/hour to meters/second in order to make my conclusions.
Suzanne
>In a message dated 2/28/2002 12:17:09 PM Eastern Standard Time, >suzanne@mathforum.com writes: > > >> This time 2:20.8 (minutes: seconds) is 140.8 seconds >> If you divide 1500 meters by 140.8 seconds you get 10.653409 meters/second >> Because you start with 140.8 (4 significant digits) then the thought >> is you would round off that answer to 10.65 meters/second. >> >> I could continue, but it is that "rounding off" part that I'm >> interested in discussing. >> > > >Rounding off should always be the LAST thing you do before you put the box >around your answer. Computations should be done with at least one more >significant digit than you want in your final answer. > > >You should continue the computation 10.653409 * 1 mile / 1609.344 meters * >3600 seconds / 1 hour = 23.83099723 miles / hour < 25 and really no round off >necessary to answer your question. Rounding now gives 23.83 miles / hour. > >Assuming 1500 is correct to at least four digits, 140.8 has four, 3600 is >exact, the 1s are exact and 1609.344 has seven. The answer is accurate to no >more than four digits. However to answer the speed limit question (< or >) >you need even less. > > >Lin > >Lin McMullin >Niantic, CT.
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