42

eh … OK then. 16.

Could also be written in a more classical way like:

 8                   8 ( 1 + 3 )      8 + 24      32
--- (1 + 3) = -------------- = ---------- = ----- = 16
 2                          2                  2             2

One could of course also take the simpler / more direct? approach with normal precedence and associativity, (here from K&R p. 53 (p. 66 in PDF))

* Parenthesis have highest precedence in the given exercise

* Division and multiplication have same, and are applied left to right

    8 ∕ 2 × (1 + 3)
= 8 / 2 × 4
= 4 × 4
= 16

or, if you like:

     8 ∕ 2  × (1 + 3)
= (8 / 2) × (1 + 3)
= 4 × 4
= 16

or:

    8 ∕ 2 × (1 + 3)
= 4 × (1 + 3)
= 4 + 12
= 16

etc.

The ANSWER IS 16!! 😜

Interesting puzzle.  This type of ambiguous math question has been widely discussed.  And the big problem - is the ambiguity.   

Order of operations as taught by mnemonic device, in schools, states the answer would be 16.   

BUT the math community at large could instead state that the question is inherently ambiguous, and if a single answer is required, the ambiguity should be resolved by adding parenthesis, before requesting an answer.   

The answer can be 16 (commonly), but it could also be argued to be 1.   Both could have valid arguments.  If I were pressed to give an answer to this ambiguous equation -- the answer would be 16 (with x degree of probability) or 1 (with y degree of probability).  Since Math describes situations - both answers could be correct.

Hello Jarls!

We have an exercise for you that seems easy only at first glance. Can you solve it and explain your answer? 

8\2(1+3)=16

1+3=4

8/2=4

2 + 6=8. divided by 8=1 one is the answer 

Parenthesis first-- THEN Division/Multiplication from LEFT to Right:

Therefore:

8÷2(1+3)

rewritten as:

8÷2×(4)

The only way to get 1 is if the equation was 

8÷(2(1+3)).

Answer is 1

Please Excuse My Dear Aunt Sally

Parenthesis, Exponents, Multiplication, Division, Adding, Subtraction

(1+3)=4, 2x4=8, 8÷8=1

    8            8           8
--------  = -------- = ------- = 1
2(1+3)      2(4)        8 

I am surprised this thread has lasted so long, but you are right it would be nice as to which is the right answer,according to the administrator who posed the question.

However, I suspect that wouldnt be the end of it, as both answers are correct, depending on which ever system you use to solve it ,which I think was the whole point of the riddle.

Lots of mathematical and scientific information has been refined over the years such that old definitions strictly speaking no longer apply,though those outside these fields still probably might remember them or use them.

BEDMAS

8/2(1+3)

8/2(4)

4*4

=16

1 !

8    /   2   (1+3)  

First the long explanation:

Note: The parenthesis coming directly after the 2 means that the amount within the brackets is to be multiplied by 2 . There is no nothing there to separate them.  i.e. 8 / 2(1+3)  is not the same as 8 / 2 x (1+3) . If you inserted the symbol you added something that was not part of the original equation in the question. Even then there would need to be brackets around the (8/2) in order for the 2 not to be distributed over the (1+3).

Everything after the division sign in this particular equation must be dived into the 8.

The proof first.

lets say x = 1 and y = 3  too make it easier to see for now. 

=      8  /   2 (x+ y)      

Solve for x and y:

Divide all by 2:

becomes

= 4 / (x+y)

OR:

          4

=  _________    

         (x+y) 

Multiply all by (x+y) to get x+y on one side of the equation and isolate the sub-equation.

becomes   (x+y)  =  4  x ( (x+y)/(x+y))

since anything divided by itself is 1 becomes simplified as

---->(x+y)  = 4 (1)

Divide all by 4:

becomes:  (x+y) /4 = 4/4

simplified is   (x+y) / 4 = 1

which when we substitute back in the 1 for the x and 3 for the y is 

(1+3)     

_____  = 1   TRUE Statement

4

gives us 1 = 1    ---- > Hence the correct answer is one. (1)

Brackets when incorporated in math equations denote superiority and must be dealt with first. The leading 2 in front of the brackets without a multiplication symbol indicates the integer or whatever  must be distributed over the contents inside the brackets. The 2 in this case.

2(x+y) == 2x + 2y  proof put the numbers back in temporarily  2(1+3) == 2 x 1 + 2 x 3    OR   2(4) == 2+6   ==>    8 = 8  See...

Let's proceed.

So a faster method:

   8 / 2 (x+y)    

= 8 /(2x +2y) ;            You must distribute the 2 across the contents inside the brackets. 

                                   WHY? Rules. Don't add something not there. You are dividing 8 by 2 groups of (x+y) or (1+3) in this case. 

=   8 /((2x1) +(2x3))   ; you can't lose your outside brackets when distributing be careful as you are basically breaking 

                                    the brackets down here. It is the opposite of fusing runes.

= 8 / (2+6)

= 8/8

= 1

You cannot add symbols to an equation which will change the equation do what you would like it to be.

 8 / 2(1+3) is not the same as 8 / 2 x (1+3) 

The first one is the equation we were asked about.

The answer in the first case is 1.

 The answer in the second case is, you guessed it, 16. Which is not the one we were being asked about.

8/2(1+3)  is NOT equal to  8 / 2 x (1+3) where the 8 gets divided  by only the  2.

People get sloppy with equations and writing their symbols. Don't let that happen to you. Write what you mean.

Just for the geniuses in this thread. Multiplication is associative, division is NOT:

https://en.wikipedia.org/wiki/Associative_property

Thus,

8 * 0.5 * 4 == (8 * 0.5) * 4 == 8 * (0.5 * 4) => 16

You cannot swap the order of division and multiplication, it is not associative:

(a / b) * c != a / (b * c)

The most amazing thing is to read those with the wrong answer, who profess how all those with the correct answer are wrong!

DeathMiser said:

The most amazing thing is to read those with the wrong answer, who profess how all those with the correct answer are wrong!

lol ... maybe people should go to an online calculator and type it in exactly as written in the op (which means you need one where you can put in parenthesis) with an = at the end and then "those with the wrong answer" can argue with the online calculator

I decided to check on your advice and look on the internet.As you described it is difficult to ask the question.

On typing  8÷2(1+3) on a browser the internet converts the question to (8÷2)×(1+3)= ? Answer to (8÷2(1+3) is 16,

Answer to 8÷(2(1+3)) is 1.

As to WDYWTNTF  according to several web tutorials  hosted by whom appear to be maths teachers,there is no need for the double brackets, as the bracket would  not appear to disappear after you have completed the operation inside. So CIM what is your answer? 

Given the internet's different appraisal the argument continues!?

Did Plarium steal the puzzle  directly from the internet, where the answers given are as similarly contradictory ?

htps://www.quora.com/What-is-the-answer-of-8-2-1-3