Re: it's just simple questions..please answer these.

On 24 Nov 2005 23:23:13 -0800, "yakuza" <koninja@xxxxxxxxxxx> wrote:

>hi nice to see all of you here this group
>I've got some problems in doing mathematics. and they are so simple
>so please don't go off now~~!
>first of all the statement of the exercise is 'perform the indicated
>operations on a calculator. Assume that all numbers are approximate.'
>and the problems are
>
>1. 3.168 + 53.91 ÷ (-17.85)
>2. 0.0350 - 0.0450/1.909 <---- as you knew, on
>the right is a fraction.
>
>as you knew
>
>the operations with approximate numbers
>1. When approximate numbers are added or subtracted, the result is
>expressed with the precision of the least precise number.
>2. When approximate numbers are multiplied or divided, the result is
>expressed with the accuracy of the least accurate number.
>3. When the root of an approximate number is found, the result is
>expressed with the accuracy of the number.
>and in the addition, where there is a combination of operations, the
>final operation determines how the final result is to be rounded off.
>for instance,
>in 38.3 - 12.9(-3.58) = 84.482, we know that
> 38.3 - 12.9(-3.58) = 38.3 + 46.182 = 84.482
>if those numbers are approximate, we must round off the result to
>tenths, which means the sum is 84.5
>(if my explanations are not sufficient then request more and then I'll
>do more)
>in the book, the solutions are written as
>
>1. 0.148
>2. 0.0114
>
>do you think it is right? I think it is strange. I think the solutions
>to them is to be written as
>
>1. 0.15
>2. 0.011
>
>what do you think of it???????????????????????????????????????
>please give some advice about it.

Your book should discuss 'significant digits' or 'significant
figures', and 'decimal places'.

These links should help:
http://mathworld.wolfram.com/SignificantDigits.html
http://www.physics.uoguelph.ca/tutorials/sig_fig/SIG_dig.htm


Problem 1. 3.168 + 53.91 ÷ (-17.85)

53.91 / (-17.85) => -3.020
3.168 + (-3.020) => 0.148


Problem 2. 0.0350 - 0.0450/1.909

0.0450 / 1.909 => 0.0236
0.0350 - 0.0236 => 0.0114

It is not correct to 'round' intermediate calculations the way I did
here. I did it anyway as my best attempt to show why your book gives
the answers it does.

.

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