+0

# 8 : 2 ( 2 + 2 ) = ?

0
276
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8 : 2 ( 2 + 2 ) = ?

https://uk.yahoo.com/style/maths-problem-dividing-internet-whats-152957777.html

Aug 2, 2019

#1
+1666
+4

If the 8 is a question number:

I would solve it like this:

2(2+2)

2(4)

2*4

8

If the 8 is part of a ratio/proportion thingy:

8/(2(2+2))

8/(2(4))

8/8

1

Aug 2, 2019
edited by tommarvoloriddle  Aug 2, 2019
#2
+105683
+2

I can't access that site but

8:8

is

1:1

Aug 2, 2019
#3
+1666
+1

is it a ratio or is a question number?

tommarvoloriddle  Aug 2, 2019
#4
+105683
+1

It is presented as a ratio.

Melody  Aug 2, 2019
#5
+19832
+1

This was in the news yesterday-ish

(you have a typo in your question)

8/2(2+2) = ?      (edited...I had a typo in MY answer too!   I had posted :  8*2(2+2) = ? )

PEDMAS   says it's 1

BODMAS  says it's 16

See:

https://www.foxnews.com/tech/viral-math-problem-baffles-many-internet

Aug 2, 2019
edited by ElectricPavlov  Aug 2, 2019
edited by ElectricPavlov  Aug 3, 2019
#6
+8810
+4

Thanks EP for that link, but I'm pretty sure the information in that article is definitely incorrect.

The question is:

$$8\div2(2+2)\ =\ ?$$

And the ONLY correct answer is:

$$8\div2(2+2)\ =\ 8\div2(4)\ =\ \dfrac82(4)\ =\ 4(4)\ =\ 16$$

See here that WolframAlpha says the answer is 16:

https://www.wolframalpha.com/input/?i=8%C3%B72(2%2B2)

PEMDAS and BODMAS mean the same thing, and they both say it's 16.

Parenthesses and Brackets are the same thing. Exponents and Orders are the same thing.

Multiplication and Division are on the same level and so can be written either as MD or DM.

We are also taught that when two operations are on the same level, we do them "left to right".

Notice that he writes Mult/Div on one line and Add/Sub on one line.

And especially watch the example that starts around the time 4:10

Aug 3, 2019
edited by hectictar  Aug 3, 2019
#13
+19832
+1

I would call it 16 also .....   shows the importance of SYNTAX and brackets and parentheses to convey EXACTLY what you intend.....hate launch a rocket to Mars with ambiguity like this in the telemetry !

8 / (2 (2+2))  = 1

8 / 2 (2+2)    in my book = 16

ElectricPavlov  Aug 3, 2019
#7
+8810
+4

The left-to-right rule does work for evaluating these expressions. However, in the case of division, instead of thinking that operations on the same level are done "left to right," I prefer to think that only the "item" immediately following the division symbol goes in the denominator, where an "item" is either a number or an expression enclosed in parenthesees.

The expression   $$1\div2+3+4$$   is equal to   $$\frac12+3+4$$   because we place

only the item immediately following the division symbol,  2 ,  in the denominator.

The expression   $$1\div(2+3)+4$$   is equal to   $$\frac{1}{(2+3)}+4$$   because we place

only the item immediately following the division symbol,  (2 + 3) ,  in the denominator.

Following this rule also means the expression   $$12/6/3$$   is equal to   $$\dfrac{\frac{12}{6}}{3}$$   which is  $$\dfrac23$$

The alternative rule would be that everything after the division symbol goes the denominator.

I personally do not like to say we must follow "left to right" because

for expressions like this:  1 + 2 + 3 + 4 + 5

we don't have to follow left to right. We could evaluate it like this:

1 + 2 + 3 + 4 + 5   =   1 + 2 + 3 + 9   =   1 + 5 + 9   =   10 + 5   =   15

It doesn't hurt to follow left-to-right to evaluate that expression; it just isn't necessary.

Another reason I prefer the rule "only use the item immediatley adjacent to the operator as the operand" is that we can use a similar rule for exponents. In the case of exponents, the rule would be "only the item immediately preceding the caret is the base."

4^2^3

Should  4^2^3  be  4^(2^3)  or  should it be  (4^2)^3   ?

If we just stick with the left-to-right rule, we would get

4^2^3  =  16^3  =  4096

If we use the rule "only the item immediately preceding the caret is the base," we would get

4^2^3  =  4^8  =  65536

Here, WolframAlpha says the answer is  65536:

https://www.wolframalpha.com/input/?i=4%5E2%5E3

The only operations that need such a rule are division, exponentiation, and subtraction.

Aug 3, 2019
#8
+105683
+1

They are great teaching post Hectictar :)

Aug 3, 2019
#9
+8810
+3

Thank you Melody!

I just found this:

https://www.quora.com/What-is-the-difference-between-BODMAS-and-PEDMAS

According to the answer there,  a/bc  means  a/(bc)  which goes against my idea.

Hmm, I don't like that! But I guess it is the case. Though I still think  1/4(3)  =  3/4

hectictar  Aug 3, 2019
#10
+105683
+1

Yea I think those 'technicalities' are really confusing.

who knows what a/bc means  I think brackets are needed!

Melody  Aug 3, 2019
#12
+1808
+2

This debate seems perpetual. The issue returns at least once every school year.

https://web2.0calc.com/questions/help-with-pemdas

---------

Another reason I prefer the rule "only use the item immediatley adjacent to the operator as the operand" is that we can use a similar rule for exponents. In the case of exponents, the rule would be "only the item immediately preceding the caret is the base."

4^2^3

Should  4^2^3  be  4^(2^3)  or  should it be  (4^2)^3   ?

If we just stick with the left-to-right rule, we would get

4^2^3  =  16^3  =  4096

Note that the web2.0calc calculator resolves this from the left to right or ascending order, where the resultant product becomes the BASE of the next exponent.  This operation is easy to see in the display above the calculator.  This is the only exception to the hierarchical order of operations. The reason for this is probably because the standard product of exponents to a base is well more common in physics and engineering than conventional stacked powers.

If we use the rule "only the item immediately preceding the caret is the base," we would get

4^2^3  =  4^8  =  65536

Here, WolframAlpha says the answer is  65536:

Wolfram follows the (official) stacked power convention, where stacked powers are (exponentially) multiplied from the right to left (from the top down), and the resultant product becomes the EXPONENT to the base number. Generally, stacked power and power-towers are used in advanced, theoretical mathematics.

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According to the answer there,  a/bc  means  a/(bc)  which goes against my idea.

Hmm, I don't like that! But I guess it is the case. Though I still think  1/4(3)  =  3/4

For a/bc, the convention will equal a/(bc)

Implicit multiplication of variables takes precedents over division – a noted exception, dating back to the late 1960s, to the normal convention of mathematical hierarchy. Herr Massow’s calculator is the only one I know of that that does this, and it’s probably because it allows the use of variables. (Comments from LancelotLink –2015)

Pasting a=20;b=2;c=5; a/(b)(c) in the calculator will result in (2).

Pasting 20/2*5 in the calculator will result in (50)

Note that pasting 20/(2)(5) will result in (2),  but pasting this 20/(2)*(5) will result in (50). The parenthesis without an operator between them triggers the variable precedents.

Note also, that the convention for precedents of variables multiplication applies only to the first two variables.

Posts related to hierarchy-order of operations:

https://web2.0calc.com/questions/help-with-pemdas

https://web2.0calc.com/questions/4-2-x-2-2-x-56#r8

GA

Aug 3, 2019
edited by GingerAle  Aug 3, 2019
#14
+105683
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ok, still I think when there is possible confusion (over and above knowing the very basic rules) people should just use brackets.

That indice one gets me every time!

Melody  Aug 4, 2019
#15
+19832
+1

AGREED !  UNfortunately....we get a lot of folks posting stuf which is UNclear!   Parentheses and brackets are NECESSARY to get correct answers to postings (and not make an engineering mistake that kills people !)          ~EP

ElectricPavlov  Aug 4, 2019
#17
+1808
+2

... UNfortunately....we get a lot of folks posting stuf which is UNclear!   Parentheses and brackets are NECESSARY to get correct answers to postings (and not make an engineering mistake that kills people !)

------

I agree that the postings from many students are unclear. It’s obvious these students lack the prerequisites for the posted questions; including an understanding of basic mathematical hierarchical conventions. Without these prerequisites, they will not understand where to place parenthetical operators, or they believe them to be unnecessary even when included in the original question.

These deficits point to an apparent flaw in lower-level education of students for these hierarchical conventions. Based on my observations, the debate on these conventions are usually by second-year college/university students and reaches a crescendo every other year. It may be because the crescendo carries over to first year students, that when they become second-year students it’s mostly a moot point and last year’s news.

As for engineers, especially those who have the credentials and experience to create or certify anything that might cause death to a population, or the destruction of expensive science experiments, it’s reasonable to assume they are well versed on such hierarchies. In addition, all mathematics and algorithms are peer reviewed and subjected to tests to catch transient math and logic errors.  This process works well, as indicated by the rare failure. Most failures, when they occur, are usually traceable to a sequence of errors where no single event by itself would have caused the failure.

In modern computing, redundant uses of parenthetical operators are a trivial matter, but in the early days of computerized control, mnemonic and variable storage space was always at a premium and maxed-out, so superfluous parenthetical operators were not an option.

The article below gives insight to the computer related testing and contingency plans in use for the Apollo 11 moon landing.

I think it is fascinating we could land men on the moon, collect samples, and bring everything back intact, in an era when the population standard thought of computers and space travel as mostly science fiction. It’s a tribute to the hierarchy of human intelligence—never forgetting the occasional genetically enhanced chimp.

GA

GingerAle  Aug 4, 2019
edited by GingerAle  Aug 4, 2019
#18
+105683
+1

I remember looking into the night sky to see if I could spot Apollo 11.

I have lived in a wondrous era !

I wonder what the next century has in store for the children of today!

Can technological advances continue at the same acceleration?  My mind bogges.

Next year we are getting a air taxi service in Melbourne.  The craft will land on many key buiding tops.

soon it will be like the Jetson's!