U.S. CitiesCity-Data Forum Index
Go Back   City-Data Forum > General Forums > Science and Technology
 [Register]
Please register to participate in our discussions with 1.5 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
Jump to a detailed profile or search
site with Google Custom Search

Search Forums  (Advanced)
Business Search - 14 Million verified businesses
Search for:  near: 
Reply Start New Thread
 
Old 05-21-2011, 03:59 PM
 
Location: SWUS
5,393 posts, read 4,265,736 times
Reputation: 5633
So, if that way is wrong, enlighten us as to the correct way? of course, it's very probable that I'm getting something mixed up somewhere, as I really could not care less about math.
Reply With Quote Quick reply to this message

 
Old 05-21-2011, 03:59 PM
 
Location: Wyoming
6,654 posts, read 8,530,608 times
Reputation: 8608
Quote:
Originally Posted by Charles View Post
It is interesting how may people immediately think the answer is 2. How many times has this burned people?
It sure got me. (I'm still not too sure.)
Reply With Quote Quick reply to this message
 
Old 05-21-2011, 04:28 PM
 
Location: Chicago
3,066 posts, read 3,088,812 times
Reputation: 1905
Quote:
Originally Posted by Gantz View Post
After you get to 48÷2(12) you have to do 48÷2 first, because division comes before multiplication in this case.
48÷2(9+3)
48÷2(12)
24(12)
288

You'd get 2 only if you had 48÷(2(9+3)) - in math if you want to express division as a denominator you have to use extra parenthesis.

48÷(2(9+3))
48÷(2*12)
48÷24
2
Multiplication comes first.
I am correct.

Apparently Hitler agrees with you

Reply With Quote Quick reply to this message
 
Old 05-21-2011, 05:49 PM
 
20,273 posts, read 15,004,076 times
Reputation: 9306
Quote:
Originally Posted by Alacran View Post
Multiplication comes first.
I am correct.

Apparently Hitler agrees with you

Right, multiplication comes before addition. That's why it's 288. Hitler was one of the smartest people, I don't get why him agreeing on a math problem could be insulting.
Reply With Quote Quick reply to this message
 
Old 05-21-2011, 06:08 PM
 
Location: Chicago
3,066 posts, read 3,088,812 times
Reputation: 1905
Quote:
Originally Posted by NJBest View Post
Right, multiplication comes before addition. That's why it's 288. Hitler was one of the smartest people, I don't get why him agreeing on a math problem could be insulting.
48÷2(9+3)

48/2(9+3)

48
2(9+3)


48
2(12)

48
24

2

Can I make it any simpler???
Reply With Quote Quick reply to this message
 
Old 05-21-2011, 06:25 PM
 
Location: Victoria TX
38,741 posts, read 36,414,540 times
Reputation: 28632
Quote:
Originally Posted by infiri View Post
48 * (9+3), this would be the same equation,
2


Not the same as

48
2(9+3)

2 different things...



You are correct. The sign " ÷ " is non-standard in algebra, and is rarely if ever used, precisely because it is ambiguous. It is used only in arithmetic. In algebraic notation, the division command is always the straight line, with elements above the line to be divided unambiguously by elements below the line. Just as the " x " is never used to command multiplication. Several members expressed serially, which may or may not be parenthesized, are understood to be multiplied, and two members above and below the line are understood to be divided. That is the standard algebraic notation, and anything else does not conform.

The sumbol " ÷ " is a convenience, to be used where an above and below line is inconvenient. It means that the expression to the left of the sign is to be divided by the expression to the right of the sign. Therefore, it unambiguously means

48
2(9+3)

You can't have it any other way. If you are going to use " ÷ ", you MUST place the 48 and the 2 in parentheses, since you have abandoned the line to show division, and there is no longer an unambiguous statement about the division process.

The original problem was not stated using algebraic symbols, and therefore cannot be categorically resolved.

Let a=2, b=9, and c=3. Express is at 48 ÷ a(b+c), and you will see how clear it becomes. a(b+c) is obviously ab+ac, or 18+6, or 24. Does everybody agree that you resolve the parentheses first? That is exactly what I just did. Than, after resolving the parentheses, you proceed to your division.

Last edited by jtur88; 05-21-2011 at 06:51 PM..
Reply With Quote Quick reply to this message
 
Old 05-21-2011, 06:27 PM
 
20,273 posts, read 15,004,076 times
Reputation: 9306
Quote:
Originally Posted by Alacran View Post
48÷2(9+3)

48/2(9+3)

48
2(9+3)


48
2(12)

48
24

2

Can I make it any simpler???
No, that's simple enough. Where you go wrong is between the first and second line. You drop down the (9+3) below the 48 along with the 2.

48÷2(9+3)

48 x .5(9+3) [Remember that division is just multiplication of inverse. The inverse of 2 is 1/2 or .5]*

48 x .5(12) [Add what's in the parenthesis)

24(12) [Start multiplying left to right.]

288 [Finish]

* Since division is really just multiplication of inverse, it's on the same rank. Just like how subtraction is justs addition of a negative number.

I think that people here are thinking that multiplication is higher rank than division. But that is not the case. Multiplication comes before addition, but not division.

This confusion is precisely why infix expression should be avoided. I don't know why they still use that as the primary method of teaching algebra in school.
Reply With Quote Quick reply to this message
 
Old 05-21-2011, 06:37 PM
 
9,923 posts, read 7,040,546 times
Reputation: 7973
Quote:
Originally Posted by Csiko View Post
Order of operations: PEMDAS

Multiplication comes before division, therefore 2 and 12 are multiplied before you would divide from 48.
This is 4th grade stuff, people.


edit: Nevermind, apparently there are people in this country that actually read M/D and then A/S from left to right. so I guess it depends on how you were taught and how your teacher interpretted it.
PEMDAS does NOT mean that Multiplication comes before division, nor does it mean that addition comes before subtraction.

Order of Operations - PEMDAS

Quote:
P
Parentheses first
E
Exponents (ie Powers and Square Roots, etc.)
MD
Multiplication and Division (left-to-right)
AS
Addition and Subtraction (left-to-right)
This is Algebra I

Quote:
Divide and Multiply rank equally (and go left to right).

Add and Subtract rank equally (and go left to right)
Reply With Quote Quick reply to this message
 
Old 05-21-2011, 06:58 PM
 
Location: Victoria TX
38,741 posts, read 36,414,540 times
Reputation: 28632
Please refer to this chart:
Algebra symbols list

You will see that " ÷ " is not on the chart of Algebraic symbols. Therefore, there is no algebraic rule about how do resolve a problem using a non-standard symbol. The solver is left to guess that the symbol means.
Reply With Quote Quick reply to this message
 
Old 05-21-2011, 07:06 PM
 
20,273 posts, read 15,004,076 times
Reputation: 9306
Quote:
Originally Posted by jtur88 View Post
Please refer to this chart:
Algebra symbols list

You will see that " ÷ " is not on the chart of Algebraic symbols. Therefore, there is no algebraic rule about how do resolve a problem using a non-standard symbol. The solver is left to guess that the symbol means.
According to that list, +,-,/,* are not algebraic symbols either. Seriously, algebra includes the basic math symbols. The ones on that list are just the ones that are brought to the table by algebra.
Reply With Quote Quick reply to this message
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.

Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.


Reply
Please update this thread with any new information or opinions. This open thread is still read by thousands of people, so we encourage all additional points of view.

Quick Reply
Message:


Over $84,000 in prizes was already given out to active posters on our forum and additional giveaways are planned!

Go Back   City-Data Forum > General Forums > Science and Technology
Similar Threads

All times are GMT -6.

© 2005-2014, Advameg, Inc.

City-Data.com - Archive 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 - Top