# See if you know the correct answer

Discussion in 'Community Discussion' started by BasicGreatGuy, Aug 3, 2019.

1. ### BasicGreatGuy Contributor

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#1
For grins and math giggles, see if you can find the correct answer.

8 ÷ 2(2+2) =

2. ### Apple fanboy macrumors Nehalem

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#2
1.

3. ### BasicGreatGuy thread starter Contributor

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#3

4. ### Apple fanboy macrumors Nehalem

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#4
Lol. Hardly. I was a terrible student. Never liked school. Left at 15.

5. ### BasicGreatGuy thread starter Contributor

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#5
A lot of people who went thru school don’t know the correct answer.

At least one good principle stuck in your head. I am sure there is more.

6. ### Scepticalscribe macrumors Westmere

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#6
I did it in my head and arrived at the same answer (all the while hearing in my mind the echo of my maths teacher's voice as she gave instructions on the precise sequence of steps to be followed if faced with such a problem).

But, well done.

7. ### Apple fanboy macrumors Nehalem

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#7
I tend to do most of my maths in excel these days.
--- Post Merged, Aug 3, 2019 ---
Also in my head. It’s those mornings watching countdown that help!

8. ### Scepticalscribe macrumors Westmere

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#8
My dad used to love Countdown, and sometimes, watched it in the afternoon after he retired.

9. ### Apple fanboy macrumors Nehalem

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#9
We watch the repeat in the mornings around 5:30 am. I’m shocking at the letters rounds, but sometimes get the numbers.

10. ### Scepticalscribe macrumors Westmere

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#10
Actually, I'm normally pretty good at crosswords (my mother was a real whizz at crosswords, until dementia claimed her), but I must confess that the conundrums on countdown (in the days when I used to watch it some wet summer afternoons with my dad) usually leave me flummoxed.

### Staff Member

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Jul 1, 2014
#11
Seen several articles where math professors argue that it's just a poorly written formula, so, either is correct since sloppy work, no context.

Eg, If passing this through a compiler (syntax error aside), would generally be interpreted as 8 ÷ 2 x (2+2). This would be a left to right parsing, and basically comes out as (8 ÷ 2) x (2+2) = 16. Variations on this that is used as examples for coding is something like 4 x 5 + 6. Did you want (4 x 5) + 6, or, 4 x (5 + 6)?

But if writing scientific, 8 / 2(2+2) = 1

12. ### Mefisto macrumors 65816

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#12
Well hot dog! Even I, who at one point or another, have at first try failed practically every math class I've had since grade school, got this correct. I have several talents but math sure ain't one of them. Not something I'm particularly proud of, I'm just usually very bad at reading numbers.

So thanks @BasicGreatGuy for the feeling of accomplishment!

13. ### MacDawg macrumors Core

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#13
Winner, winner, chicken dinner

14. ### Gutwrench Contributor

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Jan 2, 2011
#14
All one needs to know to correctly solve the problem in the op is the order of operation.

### Staff Member

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#15
That is what I was thinking also.

PEMDAS gets you 1.

Parenthesis, exponents, multiply and divide (L to R), then addition and subtraction (L to R).

16. ### Gutwrench Contributor

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Jan 2, 2011
#16
This topic needs moved to PRSI.

### Staff Member

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bedlam
#17
In a programming language like Forth, or using RPN, there's no need for operator precedence. It's unambiguous and parenthesis-free:
8 2 2 2 + * / . \ the . prints number on top of stack, and \ is comment to end of line
8 2 / 2 2 + * . \ a different series of operands and operators, so different result

18. ### TheAppleFairy macrumors 68020

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The Clinton Archipelago unfortunately
#18
It's clearly 16. Not sure how anyone is getting 1.
--- Post Merged, Aug 3, 2019 ---

PEMDAS is right but you executed it wrong. After you do the parenthesis the rest is left to right... So 8 divided by 2 then multiply it by 4 gets you 16.

19. ### BasicGreatGuy thread starter Contributor

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#19
(2+2) = 4
2(4) = 8
8 / 8 = 1

20. ### TheAppleFairy macrumors 68020

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#20

Nope that's wrong.

8 ÷ 2(2+2) =

8 ÷ 2(4) =
now you go left to right

8 ÷ 2 is 4
4(4)= 16.

### Staff Member

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#21
I think you may be correct. It says M and D left to right, not M then D.

22. Aug 3, 2019
Last edited: Aug 3, 2019

Joined:
Sep 21, 2012
Location:
In the middle of several books.
#22
You get 16 if you drop the parenthesis. However, dropping the parenthesis is wrong. It stays intact because it is part of the first step of PEDMAS.

8/2(2x2)
8/2(4)
8/8=1

You were solving the equation as (8/2)*(2x2) which is a different equation than what I posted, in my opinion.
--- Post Merged, Aug 3, 2019 ---
Where is @Doctor Q ?

23. ### TheAppleFairy macrumors 68020

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The Clinton Archipelago unfortunately
#23

why are you multiplying the 2 and the (4) before dividing the 8 by 2? you must go left to right after you do what's INSIDE the parenthesis. FYI I am 100% sure of myself, I have always been great at math.

24. Aug 3, 2019
Last edited: Aug 3, 2019

### Gutwrench Contributor

Joined:
Jan 2, 2011
#24
Exactly. Modern order of operation.
--- Post Merged, Aug 3, 2019 ---
Enthusiastically agree. Multiplication and division are the same precedence therefore it’s left to right after the parens.

### Staff Member

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#25
https://en.wikipedia.org/wiki/Order_of_operations#Mixed_division_and_multiplication

Similarly, there can be ambiguity in the use of the slash symbol / in expressions such as 1/2x.[5] If one rewrites this expression as 1 ÷ 2x and then interprets the division symbol as indicating multiplication by the reciprocal, this becomes:

1 ÷ 2 × x = 1 × 1/2 × x = 1

With this interpretation 1 ÷ 2x is equal to (1 ÷ 2)x.[1][6] However, in some of the academic literature, multiplication denoted by juxtaposition (also known as implied multiplication) is interpreted as having higher precedence than division, so that 1 ÷ 2x equals 1 ÷ (2x), not (1 ÷ 2)x.

For example, the manuscript submission instructions for the Physical Review journals state that multiplication is of higher precedence than division with a slash,[7] and this is also the convention observed in prominent physics textbooks such as the Course of Theoretical Physics by Landau and Lifshitz and the Feynman Lectures on Physics.[a]

To settle this, we might need to bring in... the Comfy Chair.