Ordering confusion  TOPIC_SOLVED

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Ordering confusion

Postby firkinfedup on Tue Sep 25, 2012 8:00 pm

Hi there, I'm trying to relearn Algebra from the ground up, and its been a long time so I have a bit of a noobish question regarding an equation in the book I'm reading.

So it says to use the ordering system, PEMDAS

Parentheses
Exponents
Multiplications
Divisions
Addition
Subtraction

Now given the following...

9 / 3 x 7 - 2^3 + 7

Following the rules as above, I would do 2^3 and then 3 x 7. But this is wrong, so my confusion is why the division comes before the first multiplication or is it simply a matter of how it's written?

If I type it into Wolfram it changes it so its 9 3rds, rather than 9 divided by 3 that is actually written in the book, using the division symbol that I can't type on this iPad.

When given this symbol do I always express it as a fraction to the whole number on its right prior to any other operators?

:confused:


Thanks in advance for any help!
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  TOPIC_SOLVED

Postby stapel_eliz on Tue Sep 25, 2012 8:20 pm

firkinfedup wrote:Now given the following...

9 / 3 x 7 - 2^3 + 7

Following the rules as above, I would do 2^3 and then 3 x 7. But this is wrong, so my confusion is why the division comes before the first multiplication or is it simply a matter of how it's written?

This is exactly the ambiguity discussed in the last example at the bottom of this page. If the expression were "9/(3*7)", the meaning would be clear; as it is, it probably means "(9/3)*7". But "the" answer will vary with the technology (Excel, a TI-83, etc) or the source (a friend, two different instructors, etc).
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Re:

Postby firkinfedup on Tue Sep 25, 2012 8:26 pm

stapel_eliz wrote:
firkinfedup wrote:Now given the following...

9 / 3 x 7 - 2^3 + 7

Following the rules as above, I would do 2^3 and then 3 x 7. But this is wrong, so my confusion is why the division comes before the first multiplication or is it simply a matter of how it's written?

This is exactly the ambiguity discussed in the last example at the bottom of this page. If the expression were "9/(3*7)", the meaning would be clear; as it is, it probably means "(9/3)*7". But "the" answer will vary with the technology (Excel, a TI-83, etc) or the source (a friend, two different instructors, etc).


Excellent thank you, that's extremely helpful, ill bookmark that page as no doubt ill need it again! :thumb:
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Joined: Tue Sep 25, 2012 7:52 pm


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