Post by: evaporade on July 07, 2009, 09:33:21 pm
Post by: monokekie on July 07, 2009, 09:43:40 pm
117====> 3 sig fig
Post by: evaporade on July 07, 2009, 09:51:57 pm
Post by: shinny on July 07, 2009, 09:56:15 pm
Post by: monokekie on July 07, 2009, 09:59:08 pm
Post by: evaporade on July 07, 2009, 10:06:42 pm
Post by: shinny on July 07, 2009, 10:08:51 pm
there are 17 rows and each row has 117 poles. How many poles are there?I think you're getting confused with the application of sig figs. You don't need to consider them here.
Post by: evaporade on July 07, 2009, 10:13:24 pm
Post by: evaporade on July 07, 2009, 10:30:42 pm
Post by: shinny on July 07, 2009, 10:41:13 pm
So when do you think you need to consider significant figures?When you're working with non-discrete values I assume. A quick googling seems to prove this. So unless you start to consider the possibility of having half a pole or something, I wouldn't really consider any need for sig figs for a calculation like that.
Post by: evaporade on July 07, 2009, 10:48:42 pm
17 X 1.170 = 2.0 X 10 metres is wrong.
Post by: shinny on July 07, 2009, 10:55:15 pm
Once again you always do when working with measured quantities. To know why, you need to understand the meaning and use of significant figures. By the way,
17 X 1.170 = 2.0 X 10 metres is wrong.
Oh whoops, contradicted myself by counting the sig figs in 17 (which you stated was exactly anyhow). 19.89 metres then. However, for discrete objects, my assumption is that there's no margin of error (unless the person counting can't count) and you don't consider sig figs. A few other sources which agree are;
Quote from: http://www.statemaster.com/encyclopedia/Significant-digits
Note that exact numbers obtained by counting discrete objects are not subject to the rules of significant figures and should be expressed as exact integers.
And from Victorian Science themselves;
Quote from: http://www.vicscience.com/vcechem/Yr12Notes/miscel/sigfigs.pdf
Unless we are counting discrete, known quantities such as the number of students enrolled at the school, when we measure quantities on instruments, the last figure in the measurement is usually uncertain.
Post by: evaporade on July 07, 2009, 11:08:12 pm
Quote from: http://www.statemaster.com/encyclopedia/Significant-digits
Note that exact numbers obtained by counting discrete objects are not subject to the rules of significant figures and should be expressed as exact integers.
This is just a lazy way to deal with significant figures.
A natural number has infinite number of significant figures.
For example 17 = 16.99999999999999......................
Back to the original question.
17 has infinite number of s.f.
117 has infinite number of s.f.
Hence 17 x 117 = 1989 has infinite number of s.f.
So there is no need to make any exceptions. You always do when working with measured quantities.
Post by: shinny on July 07, 2009, 11:15:45 pm
Once again you always do when working with measured quantities.
Quote from: http://www.statemaster.com/encyclopedia/Significant-digits
Note that exact numbers obtained by counting discrete objects are not subject to the rules of significant figures and should be expressed as exact integers.
This is just a lazy way to deal with significant figures.
A natural number has infinite number of significant figures.
For example 17 = 16.99999999999999......................
Back to the original question.
17 has infinite number of s.f.
117 has infinite number of s.f.
Hence 17 x 117 = 1989 has infinite number of s.f.
So there is no need to make any exceptions. You always do when working with measured quantities.
So you asked these questions just to play people around on technicalities (of which I'm not sure I agree with anyway)? I thought you were actually looking for the answers yourselves. As for the original question, of course it depends WHERE you got these numbers from. The two clearly aren't considered to have an infinite number of sig figs if they were obtained say, from a scale which only gets accuracy to each single gram, so anything between approximately 16.5 to 17.5 would round to 17. If these numbers were obtained from this scale, clearly they don't represent something with an infinite number of sig figs. And really, if you're going to so vehemently disprove what I've said, can you give some evidence? I wouldn't mind learning something new myself, but I'm not going to change my position just because you're basically saying "that's how it is".
Post by: evaporade on July 07, 2009, 11:30:45 pm
'Note that exact numbers obtained by counting discrete objects are not subject to the rules of significant figures and should be expressed as exact integers.' This is a bit like "just do it, you'll get the right answer'.
'The two clearly aren't considered to have an infinite number of sig figs if they were obta...' I don't think you read the original question carefully enough.
By saying this 'so anything between approximately 16.5 to 17.5 would round to 17', I don't think you know how to work with sig. fig. Correctly, 17.0 .
Post by: Mao on July 08, 2009, 12:20:46 am
On a different note:
This forum is not only about getting help for some questions. One can express ideas through questions.
Though you do demonstrate a good point and you are valid in your statements, I really can't agree you are expressing ideas through questions. If you were doing that, you would elaborate when an wrong answer has been given. But of course, it was the usual style of "To know why, you need to understand the meaning and use of significant figures. "
If you would like somewhere to play others around technicalities to feel good about yourself, please find somewhere else. Otherwise, I would recommend you adopt a different style that is less condescending.
Post by: evaporade on July 08, 2009, 08:44:15 am
In this case, as you said "you do demonstrate a good point and you are valid in your statements". What about if I was wrong, do you think I can "feel good about yourself"? The questions were to lead to the situation where the prevalent ideas fall apart.
"feel good about yourself": This is a common phenomenon on this forum.
'Once again you always do when working with measured quantities. To know why, you need to understand the meaning and use of significant figures.' This may be condescending to certain people who think highly of themselves.
So what is good coming out of this? Some of the readers know a bit more about sig. fig. and use them correctly.
This is not about 'technicalities'. It was not technically wrong to say the natural number 17 has 2 sig. fig., it is simply wrong.
Glad to leave a place with lots of bigots. Good bye and have it your way.
Post by: Mao on July 08, 2009, 11:09:58 am
Thread locked.