Poll

48÷2(9+3)=

2
46 (44.7%)
288
45 (43.7%)
No definitive "correct answer"
12 (11.7%)

Total Members Voted: 100

Author Topic: 48÷2(9+3) =  (Read 41907 times)

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Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #280 on: April 19, 2011, 05:28:29 PM »
Honestly, division signs and /'s are just amateur.  Real mathematicians use horizontal lines to indicate division.

Lol?

Offline rumborak

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Re: 48÷2(9+3) =
« Reply #281 on: April 19, 2011, 05:30:59 PM »
I think given what real mathematicians works on, 48÷2(9+3) comes out to be 3+0.8i, or something.

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Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #282 on: April 19, 2011, 05:32:59 PM »
Or 2222222

Offline XJDenton

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Re: 48÷2(9+3) =
« Reply #283 on: April 19, 2011, 05:37:23 PM »
"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." - Richard Feynman

Offline Orbert

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Re: 48÷2(9+3) =
« Reply #284 on: April 19, 2011, 07:18:44 PM »
As many have pointed out, it's really completely pointless.  The rules for simplifying or evaluating an expression are only so that students learning algebra will know how to read and write the shorthand.  In an actual application, it would be pretty obvious whether you're supposed to divide or multiply first to get the correct answer.

Offline Tomislav95

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Re: 48÷2(9+3) =
« Reply #285 on: April 20, 2011, 10:50:30 AM »
I think it's 288 because we have to go one after the other :-\
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Offline slycordinator

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Re: 48÷2(9+3) =
« Reply #286 on: April 20, 2011, 08:37:10 PM »
And since I was asked, I would in fact evaluate 48÷2x as 24x. I err on the side of assuming that implied multiplication is of equal rank to normal multiplication since I've seen less mathematicians claiming otherwise.

Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #287 on: April 20, 2011, 09:05:09 PM »
sly, maybe you can help me with this

I was tutoring and a kid asked me this problem:

"Suppose a cylinder full of sugar has a mass of 5.81. When it is 3/8 full, its mass is 3.8. What is the mass of the cylinder when it is empty?"

The thing that is confusing me is that it is mass. I know volume and mass aren't the same thing, so I am unsure of how to approach this problem. Supposed to be an Algebra 1 problem and I am drawing a blank.

Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #288 on: April 20, 2011, 09:10:34 PM »
No radius or height was given, by the way, which further perplexed me. I hope I'm not missing something obvious.

Offline Orbert

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Re: 48÷2(9+3) =
« Reply #289 on: April 20, 2011, 09:27:12 PM »
That is why application problems should always include units.  When units are provided, as they should be, there's no ambiguity.

Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #290 on: April 20, 2011, 09:34:36 PM »
Let's say the units are in kilograms

Offline rumborak

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Re: 48÷2(9+3) =
« Reply #291 on: April 20, 2011, 10:03:02 PM »
Volume and mass are proportional. Whatever unit system you would use doesn't matter, it would cancel out anyway.

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Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #292 on: April 20, 2011, 10:06:23 PM »
That is what I figured, but that isn't my issue...how do I solve this? Argh, I feel dumb for not knowing this

Offline Fiery Winds

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Re: 48÷2(9+3) =
« Reply #293 on: April 20, 2011, 10:11:23 PM »
That is what I figured, but that isn't my issue...how do I solve this? Argh, I feel dumb for not knowing this

Mass of Sugar = S
Mass of Cylinder = C

S + C = 5.81
(3/8)S + C = 3.8

System of two equations.   :tup  Took me a second too.

Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #294 on: April 20, 2011, 10:14:21 PM »
*bangs head on keyboard*

I don't understand why I can do all sorts of calculus problems and these system of 2 equations algebra 1 problems always get me. There's like a gap in my knowledge there. I sorta had an idea it was gonna be a system of equations, but it eluded me.

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Offline rumborak

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Re: 48÷2(9+3) =
« Reply #295 on: April 20, 2011, 10:16:32 PM »
"Suppose a cylinder full of sugar has a mass of 5.81.

5.81 = 1.0*C+M0

1.0*C : "1.0 of the volume, times whatever conversion factor into mass"
M0 : Mass of the cylinder

Quote
When it is 3/8 full, its mass is 3.8.

3.8 = (3/8)*C + M0

From equation 1:

C = 5.81 - M0

into equation 2:

3.8 = (2/8)*(5.81-M0) + M0

<=> 3.8-(2/8)*5.81 = (6/8)*M0

<=> M0 = 3.13

Gnaah, ninja edit!!

rumborak
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Offline Implode

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Re: 48÷2(9+3) =
« Reply #296 on: April 21, 2011, 01:00:08 AM »
Hey guys. 288 is winning. Let's celebrate by me asking another argument inducing question.

So there's a plane on a conveyor belt... :neverusethis:

Offline kári

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Re: 48÷2(9+3) =
« Reply #297 on: April 21, 2011, 02:17:24 AM »
It would take off.

You and me go parallel, together and apart

Offline Jamesman42

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Re: 48÷2(9+3) =
« Reply #298 on: April 21, 2011, 08:14:37 AM »
Massive text haha get it MASSive haha oh man haha...ha


Man, I was tired last night, looking back I really should have known all that, it being mass doesn't have that much to do with setting up the system of equations...gah!

Offline adameastment

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Re: 48÷2(9+3) =
« Reply #299 on: April 21, 2011, 08:21:11 AM »
2? What? The order of operations says that in this case you do parentheses first and then divide/multiply from left to right.

48÷2(9+3) = ?
48÷2x 12 =?
24x12=?
288
In the UK it's BIDMAS

Brackets first.
Indicies next
Division
Multiplication
Addition
Subtraction...

Offline 7StringedBeast

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Re: 48÷2(9+3) =
« Reply #300 on: April 21, 2011, 08:37:44 AM »
But wouldn't that expression be the exact same thing as:

48
___

2(9+3)


So

48
_____    =  2
24


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Offline jsem

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Re: 48÷2(9+3) =
« Reply #301 on: April 21, 2011, 08:48:27 AM »
But wouldn't that expression be the exact same thing as:

48
___

2(9+3)


So

48
_____    =  2
24



No, it's not the same thing. Check my post a few pages back.

Offline adameastment

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Re: 48÷2(9+3) =
« Reply #302 on: April 21, 2011, 08:53:39 AM »
But wouldn't that expression be the exact same thing as:

48
___

2(9+3)


So

48
_____    =  2
24




Yeah, I forgot to add that bit :P

I was gonna add "So it's definitely 2" :P

Offline 7StringedBeast

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Re: 48÷2(9+3) =
« Reply #303 on: April 21, 2011, 08:54:57 AM »
To get 288 shouldnt it be (48/2)*(9+3)  Other wise, you write it the way I wrote it above ^^. 
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Offline jsem

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Re: 48÷2(9+3) =
« Reply #304 on: April 21, 2011, 08:56:21 AM »
I get it nao lol.

I automatically jumped to this conclusion:

    48
______
2(9+3)

In which case it's 2. This is the same as 48 ÷ (2(9+3)). But that was not the given though.



Offline adameastment

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Re: 48÷2(9+3) =
« Reply #305 on: April 21, 2011, 08:58:25 AM »
To get 288 shouldnt it be (48/2)*(9+3)  Other wise, you write it the way I wrote it above ^^. 
Yeah, because with the order of operations it goes something like this:

48/2(9+3) = 48/24 = 2

Offline slycordinator

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Re: 48÷2(9+3) =
« Reply #306 on: April 21, 2011, 09:08:57 AM »
To get 288 shouldnt it be (48/2)*(9+3)  Other wise, you write it the way I wrote it above ^^.  
No.
1) The equation given is 48/2(9+3). You rewrote this as 48/(2(9+3)) . You can't both say "You can only get 288 if you add some parentheses" while yourself saying that the answer is 2 while implicitly adding them in there yourself.
2) And no. You don't have to put parentheses around the 48/2 term... because multiplication and division are of equal rank and when they both occur together in an equation you do the first one that appears in it while going from left-to-right.

Offline adameastment

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Re: 48÷2(9+3) =
« Reply #307 on: April 21, 2011, 09:11:42 AM »
But in school you are told to ALWAYS expand the brackets first?

Offline slycordinator

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Re: 48÷2(9+3) =
« Reply #308 on: April 21, 2011, 09:24:34 AM »
But in school you are told to ALWAYS expand the brackets first?
And I never said otherwise. A 2 that isn't in a bracket isn't part of the bracket.

1) 48/2(9+3)
2) 48/2*(9+3)
3) 48/2*(12)
*and here, since multiplication and division are equal rank, I do the first one that appears in left-to-right, which is the division*
4) 24*(12)
5) 288

Offline Orbert

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Re: 48÷2(9+3) =
« Reply #309 on: April 21, 2011, 11:52:12 AM »
That's the dichotomy.  I've always thought the the 2 being adjacent to the (9+3) gave it some kind of precedence, but apparently there is no such rule.  So a strict application of the rules yields the above result.