Lame ass maths riddle

28064212

Dublin_Gunner wrote: »

Work from left to right, breaking the equation into sections (and using BOMDAS as your guide).

The answer is 0.6

Only if you ignore precedence and associativity rules. You do not multiply 2(5) before dividing 30 by 2. The "B" in BOMDAS only refers to operations inside brackets. 2(5) is just shorthand for 2 * 5, and 30 ÷ 2 * 5 ÷ 5 is 15

RHunce

MJRS wrote: »

I thought multiplication and division were equal priority so you just do left to right? Hence the acronym being BOMDAS or BODMAS, both are valid. Isn't this one of loads of maths problems with two provable correct answers?

Got this from the ever reliable wiki "These mnemonics may be misleading,
especially if the user is not aware that
multiplication and division are of equal
precedence, as are addition and subtraction."

What about BIRDMAS brackets, indices, roots, division, multiplication, addition and subtraction? Same answer anyway

nyarlothothep wrote: »

What is

Is it 15?

or 0.6?
...
Or is this question broken?

30÷2(2+3)÷5

30÷(2)(5)÷5

(30÷10)÷5

3÷5 = .6

Kadongy

desertstorm wrote: »

This is true for a pixel representation of a circle (but not for an actual circle of course).

Mellor

ClutchIt wrote: »

The question is broken really. Even though there is a correct way of doing it, anyone who writes an equation in that fashion is an ignoramus

nobody would write an quetion that way, the whole purpose of writing it that way is to confuse people with a weak understanding

RHunce wrote: »

What about BIRDMAS brackets, indices, roots, division, multiplication, addition and subtraction? Same answer anyway

30÷(2)(5)÷5

(30÷10)÷5

You realise that you can't get from to (30÷10)÷5
You just applied the division sign to the first 5, which is retarded.
You can't multiply 2 inside the brackets when there is a ÷ sign before it. Only + or -

30÷(2)(5)÷5
15(5)÷5

I imagine you can finish from there:rolleyes:

RHunce

Mellor wrote: »

You realise that you can't get from to (30÷10)÷5
You just applied the division sign to the first 5, which is retarded.
You can't multiply 2 inside the brackets when there is a ÷ sign before it. Only + or -

30÷(2)(5)÷5
15(5)÷5

I imagine you can finish from there:rolleyes:

My B2 in Honours Maths says otherwise :pac:

28064212

RHunce wrote: »

30÷2(2+3)÷5

30÷(2)(5)÷5

(30÷10)÷5

3÷5 = .6

Why are you multiplying (2)(5) first? How is 30÷(2)(5)÷5 any different to 30÷2*5÷5?

Again, brackets precedence only applies to operations inside the brackets

Triangla

Typed equation exactly as typed into my scientific calculator, answer is 0.6.

ManFromAtlantis

RHunce wrote: »

My B2 in Honours Maths says otherwise :pac:

what would a B2 be worth when maths was maths in the 70's or 80's ?

RHunce

Still maths pal, I'm not doing that project maths ****e, don't be bitter because you did OL

onlyrocknroll

Wow the standard of this debate has really nosedived.

28064212

RHunce wrote: »

Still maths pal, I'm not doing that project maths ****e, don't be bitter because you did OL

But you're wrong. The answer is 15. Go back and read the thread

Mellor

RHunce wrote: »

My B2 in Honours Maths says otherwise :pac:

LMFAO

Maybe if you knew what you were doing you would of goten an A2, like i did :cool:

Triangla wrote: »

Typed equation exactly as typed into my scientific calculator, answer is 0.6.

I'm not going to be so silly as to say the calculator is wrong, but I guarantee you that you typed it in wrong.
It's a well know problem, its exists in many forms.

onlyrocknroll

Mellor wrote: »

LMFAO

Maybe if you knew what you were doing you would of goten an A2, like i did :cool:



I'm not going to be so silly as to say the calculator is wrong, but I guarantee you that you typed it in wrong.
It's a well know problem, its exists in many forms.

Mellor can you please post a link that explains why your way is correct and the other is wrong. I was sure it was 15 at first until I was convinced otherwise, now it's annoying me.

28064212

onlyrocknroll wrote: »

Mellor can you please post a link that explains why your way is correct and the other is wrong. I was sure it was 15 at first until I was convinced otherwise, now it's annoying me.

What parts of these posts don't you understand?

28064212 wrote: »

It's 15. The only way it could be 0.6 is if you redefine 5(2+3) to mean (5 * (2+3)) instead of 5 * (2+3). Bracket notation for multiplication is just shorthand, it doesn't change the precedence.

30÷2(2+3)÷5
= 30÷2(5)÷5
= 30÷2*5÷5 (÷ and * have equal precedence and are left-associative, so you do them left-to-right)
= 15*5÷5
= 75÷5
= 15

The bolded part is where most people make their mistake. "Brackets first" means you calculate what is inside the brackets first. when brackets are used for multiplication it is just shorthand for *.

28064212 wrote: »

Google puts in brackets for clarification, it doesn't change the precedence. Put in 6 - 2 * 3 and it will "change" it to 6 - (2 * 3).

The only way there's ambiguity is if you change 2(5) to mean something different to 2 * 5

28064212 wrote: »

Only if you ignore precedence and associativity rules. You do not multiply 2(5) before dividing 30 by 2. The "B" in BOMDAS only refers to operations inside brackets. 2(5) is just shorthand for 2 * 5, and 30 ÷ 2 * 5 ÷ 5 is 15

28064212 wrote: »

Why are you multiplying (2)(5) first? How is 30÷(2)(5)÷5 any different to 30÷2*5÷5?

Again, brackets precedence only applies to operations inside the brackets

Triangla

http://i1193.photobucket.com/albums/aa345/myggel2011/IMAG0605.jpg

onlyrocknroll

28064212 wrote: »

What parts of these posts don't you understand?

I understand all these posts. However they are just people stated what rules they followed, rather than providing any evidence that these are the correct rules.

Can you direct me somewhere where I can read an explanation of how to solve this correctly please.

28064212

onlyrocknroll wrote: »

I understand all these posts. However they are just people stated what rules they followed, rather than providing any evidence that these are the correct rules.

Can you direct me somewhere where I can read an explanation of how to solve this correctly please.

Order of operations => Do what's inside the brackets first. All the other operations are of equal precedence (multiplication and division), so we look at...
Operator associativity => multiplication and division are both left-associative, so are performed from left-to-right

Mellor

onlyrocknroll wrote: »

I understand all these posts. However they are just people stated what rules they followed, rather than providing any evidence that these are the correct rules.

Can you direct me somewhere where I can read an explanation of how to solve this correctly please.

But anybody getting 0.6 isn't following the rules, they are bringing ÷2 inside the brackets. nowhere rules has been posted that allows that.

30÷2(2+3)÷5 so we all agree that ÷5 is at the end and the 2+3 = 5, so this is the part that is confsuing people

30÷2(5)

What people are doing is multiplying ÷2 by 5 and getting ÷10 which is wrong. If it said ÷(2(5)) it wouls be fine but it doesn't, the ÷ sign is fixed to the 2

÷2(5) = ÷2x5 = x5÷2 = x2.5

or

÷2 is the same as x(1/2) or x(.5), (.5)x(5)= x2.5


Triangla - That's interesting.
A google search suggests thats it not unheards of, casio calculators gettign confused. Apparently it's due to a built in coding to solve multiplication implied by brackets first. a rule that doesn't exist (its just the way people write) unless you believe 2(5) is different to 2x5,
I imagine if you put a x sign before the bracket it returns 15. I hope we all agree that there is no difference.

Mellor

Another one I've seen is

6÷2(1+2)

Again, you can see the same structure. The brackets draw you attention to the right, where you end up with 6÷2(3) and get 1

But it's wrong. 6÷2(3) is just shorthand. It should be re-written as 6÷2x3

It's written in a confusing way on purpose. It should never have been like that to begin with

magicianz

Its clearly 8.1.....

Thirty \ 4 + 3 \ 5

7.5 + .6

8.1 simples

Triangla

http://math.about.com/library/weekly/aa040502a.htm

Brackets are always dealt with first

= 30÷2(2+3)÷5

= 30÷2(5)÷5

= 30÷10÷5

= 0.6

30÷2(2+3)÷5 is not the same as 30÷2*(2+3)÷5

If the * was written in the initial equation the answer would be 15.

= 30÷2*(2+3)÷5

= 30÷2*(5)÷5

= 30÷2*5÷5

= 15*5÷5

= 15

The * is not written so the answer is 0.6

28064212

Triangla wrote: »

http://math.about.com/library/weekly/aa040502a.htm

Brackets are always dealt with first

That's not what the link says. The link says:

Calculations in brackets are done first

In. As in "inside". As in "not outside". Further down the page:

Simplify inside groupings of parentheses, brackets and braces first

Again, inside.

It also says:

Multiply and divide in the order the operations occur

Note the total absence of any mention of treating multiplication differently because it's written in shorthand

Bloody Nipples

The issue is that BEMDAS/BOMDAS as taught in Irish schools promotes the idea that brackets are done first, followed by exponents (no argument so far) but that multiplication and addition are given precedence over division and subtraction respectively.

Upon asking my brother, a maths science student, apparently there's another method PEMDAS (Parentheses, Exponents, Multiplication, Division, Addition, Subtraction) taught in American schools and teaches the correct method which as 28046212 has shown, gives equal weighting to both multiplication and division and works left to right according to mathematical convention. Here's the link for those demanding evidence (if you're willing to accept wikipedia :pac:)
http://en.wikipedia.org/wiki/Order_of_operations#The_standard_order_of_operations

30÷2(3+2)÷5
=30÷2(5)÷5

This is where the issues begin. Yes, there are brackets written in, no they don't give 2(5) precedence in calculations.
It can be written as 30÷2x5÷5 or 30÷2(5)÷5. It's irrelevant. The important thing is you work left to right, and it's also easier if instead of using a division sign you multiply by the reciprocal, so...

30 x 1/2 x 5 x 1/5
or 30 x 0.5 x 5 x 0.2 (to make it even simpler)
= 15 x 5 x 0.2
= 75 x 0.2
= 15

And bearing in mind people using calculators, different calculators follow different orders of operations. Most non-scientific calculators without a stack work left to right without any priority given to different operators.

Bloody Nipples

Triangla wrote: »

http://math.about.com/library/weekly/aa040502a.htm

Brackets are always dealt with first

= 30÷2(2+3)÷5

= 30÷2(5)÷5

= 30÷10÷5

= 0.6

30÷2(2+3)÷5 is not the same as 30÷2*(2+3)÷5

If the * was written in the initial equation the answer would be 15.

= 30÷2*(2+3)÷5

= 30÷2*(5)÷5

= 30÷2*5÷5

= 15*5÷5

= 15

The * is not written so the answer is 0.6

The fact that it's a D(D) instead of D x D doesn't mean anything. It's a multiplication action and should be done at the same time as division.

mikedone

superrdave

nyarlothothep wrote: »

Here's another one

-20=-20
16-36=25-45 (16-36=-20,25-45=-20)
4^2-36 = 5^2-45 (4^2=16,5^2=25)
4^2-36 = 5^2-45
4^2-2.4.9/2 = 5^2-2.5.9/2 (2.4.9/2=36,2.5.9/2=45)
4^2-2.4.9/2 +(9/2)^2 = 5^2-2.5.9/2 +(9/2)^2 (adding both the sides (9/2)^2
[4-(9/2)]^2 = [5-(9/2)]^2 (let 4=a,9/2=b)
4-(9/2) = 5-(9/2)
4 = 5
2+2 = 5

And

10x^2-19x=-6 =?

Clever.... but the wrongness comes between the steps in bold above.

If you look at it the first line says:

[-1/2]^2 = [1/2]^2

which is correct

The next line thus says if you remove the square root, the results are equal, which is incorrect

-1/2 = 1/2

not correct

the later lines to make 2+2=5 are just bull****.

Much like this troll physics:



The issue there is that the second last line is a fallacy. It is dividing by zero. 2*0 = 1*0 is correct but it does not mean 2=1.

Cathy

Bloody Nipples wrote: »

The fact that it's a D(D) instead of D x D doesn't mean anything. It's a multiplication action and should be done at the same time as division.

30÷2(2+3)÷5 = 30÷2(5)÷5

It doesn't make sense to say 30÷2(5)÷5 = 30÷2*5÷5. To me, 2(5)÷5 clearly indicates (2x5)÷5 as opposed to 2(5÷5)...

My brain hurts.

Mellor

Triangla wrote: »

Brackets are always dealt with first

of course they are, the problem is you are getting the maths wrong.

= 30÷2(2+3)÷5

= 30÷2(5)÷5

= 30÷10÷5

= 0.6

See the bolded lines, that's you mistake.
Doing the ÷2(5) part first doesn't change the answer, the problem is that you are makign a mistake.

÷2(5) = 5/2 = x2.5

It does not equalt ÷10. A simple proof would be reverse the order, ÷2(5) = (5)÷2

30÷2(2+3)÷5 is not the same as 30÷2*(2+3)÷5

em, yes it is.

Cathy wrote: »

30÷2(2+3)÷5 = 30÷2(5)÷5

It doesn't make sense to say 30÷2(5)÷5 = 30÷2*5÷5. To me, 2(5)÷5 clearly indicates (2x5)÷5 as opposed to 2(5÷5)...

My brain hurts.

Are you serious???

Of course 30÷2(5)÷5 and 30÷2*5÷5 are the same thing, even look at what you said afterwards.

2(5)÷5 clearly indicates (2x5)÷5 as opposed to 2(5÷5)...

(2x5)÷5 = (10)÷5 = 2

2(5÷5) = 2(1) = 2

The order of division doesn't matter, as long as you do it get the sums right
??????????

Nadser

Ok, know this thread is a bit old, but here's my input (degree in maths by the way)

The question is 30/2(2+3)/5

Re-write it as an algebraic problem

Let x=30, y=2, z=3, w=5
The problem becomes: x/y(y+z)/w
x/(y^2+yz)/w

Substitute in the values
30/(4+6)/5
30/10/5
3/5 = 0.6

28064212

Nadser wrote: »

Ok, know this thread is a bit old, but here's my input (degree in maths by the way)

The question is 30/2(2+3)/5

Re-write it as an algebraic problem

Why? You've made the same old mistake anyway

Nadser wrote: »

Let x=30, y=2, z=3, w=5
The problem becomes: x/y(y+z)/w
x/(y^2+yz)/w

Substitute in the values
30/(4+6)/5
30/10/5
3/5 = 0.6

In the bolded line, why have you multiplied y * (y+z) instead of executing the operations left-to-right, given that multiplication and division have the same precedence?