Brain Teaser

[red750]

OK, you got me, I didn't proofread, but when I clarified the question, (This makes the question  7 - 0 + 7, ), I replaced the 7X0 with 0.

[Marty_d]

2 hours ago, red750 said:

This is the conundrum.

 

Processing left to right,   7-7 = 0, 0x0 = 0,  0 + 7 = 7.

 

However, Americans, and I guess some others are taught that the order of processing is PEMDAS. The order is PEMDAS: Parentheses, Exponents, Multiplication, Division (from left to right), Addition, and Subtraction (from left to right).

 

So, doing multiplication first, 7 x 0 is 7.  This makes the question  7 - 0 + 7, resulting in 14.

 

So a simple sum here results in 7, but in America it is 14.    How does that work? incidentally, putting this sum into the calculator on your iPhone gives the answer 14.

What?

Everyone is taught that way, not just Americans.

There's no such thing as just solving it left to right. Parentheses first, then exponents, division/multiplication, addition/substraction.

 

 

 

Edited January 15 by Marty_d

[facthunter]

IF you want to EDUCATE that's fine by me. That's one of the main reasons I want debate and a lust for  TRUTH and the correct  answer. My motto is Never stop learning, so we are not so far apart.  I did not know "Brain Teaser" where you determine the ONLY  answer to what was in effect a  TRICK question you posed is the nicest way to go about it without any prior warnings to responders. You probably noticed I rarely respond to the Brain teaser topic but I did wait a while and nobody else was saying much.   I was  a trained Secondary Teacher and wouldn't recommend your method but it might work better face to face.  Nev

[red750]

Then why are there so many wrong answers (processed left to right) in the replies to these questions?

[Marty_d]

No idea. But maths is international, not USA vs Australia.

[red750]

OK, try these.

 

[red750]

For  those not interested in the maths question any idea on the hands catchphrase?

 

 

 

 

 

 

 

[Marty_d]

First is 39, second is -2

[red750]

That's what I got. Unfortunately these examples don't come with a correct answer, just dozens of comments on what people think they are, and there arre many different answers. I guess you have to accept the most common answer,

 

One of the things some people have difficulty with is -2². Some say 4, others say -4.

[rgmwa]

First one 39, second one 6

[rgmwa]

13 minutes ago, red750 said:

One of the things some people have difficulty with is -2². Some say 4, others say -4.

-2² means -(2²) = -4

its being confused with (-2)² = 4

[Marty_d]

A negative multplied by another negative is a positive.

I respectfully disagree with RGMWA, if the negative was outside the bracket then -4 would be correct, but a negative squared is a positive.

[rgmwa]

24 minutes ago, Marty_d said:

A negative multplied by another negative is a positive.

I respectfully disagree with RGMWA, if the negative was outside the bracket then -4 would be correct, but a negative squared is a positive.

I'm not so sure Marty. I agree that two negatives multiplied together are a positive, but 

in (-2²) the exponent is worked out first so (-2²) becomes (-(2²)) = -4

as opposed to (-2)² = (-2)x(-2) = 4

 

In the above example:

-(-2+2-2) - (-2²) becomes

-(-2) - (-4)

2 +4 = 6

 

Edited January 15 by rgmwa

[pmccarthy]

What he said. You apply the exponent first.

[Jerry_Atrick]

PEDMAS is how I was taught from, as I recall, late primary school in the 70s.. exponents were probably not taught until early secondary school

 

I don't tjinknit is an Amerucan thing but will check tomorrow- two maths PhDs work in my team

[red750]

If you use the calculator on your iPhone (I can't speak for an Android), turn the phone to landscape mode and you get more functions. Enter 10 - 12 and you get  -2.  Press the X² button and you get 4, not -4. No parentheses assumed.

[Jerry_Atrick]

Do you hit the equals button in between.. if so, that is expected as you have asked it to do that equation first and then apply the results to the next equation. If you don't it may be a setting or  it is a bug

[red750]

I honestly cannot remember being taught PEDMAS at school, and I passed Leaving Certificate Maths 1 in 1960. I really never heard of it till I started doing these maths questions on Facebook. Never had to rely on it in 29 years in the bank.

[Marty_d]

I may have to apologize here, although fiercely argued in other places too (https://math.stackexchange.com/questions/1847834/is-a-negative-number-squared-negative for example), it does appear that the exponent is resolved on the absolute number first and then the negative applied to the result.

So yes - you're right Rob!

[rgmwa]

No worries Marty. You being wrong and me being right are equally rare events. 

[red750]

3 hours ago, Jerry_Atrick said:

Do you hit the equals button in between

If you don't hit = it assumes that you are squaring the last number entered, number 12, result 144.

 

To get the required result, you have to enter  - 2 , X , -2, then you get - 4.

[red750]

As for the Catchphrase, if you watch the video, you will see this:

 

 

The catchphrase is "Old hand", as in "He's an old hand at shearing sheep."

 

 

Here's another kind of problem. Move one match to make a correct equation.

 

 

 

[facthunter]

Thats easy. 9-9=0. Nev

[facthunter]

Anybody home?  Nev

[facthunter]

Should I ring triple O?   Nev