Math(s) problem - puzzle

[dbrenth]

My teacher asked me to write a program on the board and solve it. I wrote:

230 - 220 x 0.5

and announced that the answer was 5! My teacher claimed I was incorrect, but I was not. Can you please explain it to him? Thanks Hint: My teacher was quite embarrassed when I actually said the answer out loud.

Brent

[Richard Andrew x64]

Explain what to him? You are wrong.

The difficult we do right away... ...the impossible takes slightly longer.

[Daniel Pfeffer]

You are wrong, the teacher is right. The order of precedence in mathematical operations is (mnemonic PEMDAS): Parentheses Exponentiation Multiplication & Division Addition & Subtraction If two operations have the same precedence, they are evaluated from left to right. Your problem may be rewritten as 230 - (220 x 0.5), the answer to which is obviously not 5.

Freedom is the freedom to say that two plus two make four. If that is granted, all else follows. -- 6079 Smith W.

[Kornfeld Eliyahu Peter]

Have you write 5! as answer, or it is only for us as an expression of your frustration? :-)

"The only place where Success comes before Work is in the dictionary." Vidal Sassoon, 1928 - 2012

[dbrenth]

See my hint to another responder.

Brent

[dbrenth]

That's what he thought, too, until I actually said the answer out loud. Then he was quite embarassed. Obviously, this is a puzzle with a correct solution and not a real life experience.

Brent

[dbrenth]

Ding ding ding.

Brent

[Greg Utas]

You must have said "five factorial".

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[dandy72]

I thought about that...but who provides answers as a factorial?

[Daniel Pfeffer]

"5 factorial" is not a solution; it is simply representing the answer (120) as a different equation. If you were set a problem in a mathematics test 300 - 0.5 x 150 and answered that it is 450 / 2, the teacher would be justified in marking it incomplete because it has not been reduced to the simplest terms.

Freedom is the freedom to say that two plus two make four. If that is granted, all else follows. -- 6079 Smith W.

[SeeSharp2]

dbrenth wrote:

the answer was 5!

five factorial. Unless you were yelling at them. :-D

[Lost User]

dbrenth wrote:

Can you please explain it to him?

Dear Teacher, dbrenth is a cocky little so and so, who needs to be taken down a peg or two. ;P

[Greg Utas]

I think it was meant as a riddle rather than something that actually happened.

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[CPallini]

You teacher was right, and told you the correct result was actually 76. Could you please tell us why?

"In testa che avete, Signor di Ceprano?" -- Rigoletto

[dandy72]

Sometimes I'm just being a little bit too literal. Daniel's answer above suggests we're both on the same page on this one. :-)

[obermd]

The answer is 120. The way you get "5" is via a flaw in all four function calculators that don't follow basic math order of operations. By the way, the Windows calculator in Standard mode has this same flaw but it works properly in scientific mode.

[obermd]

And marked down for not completing the solution.

[Fueled By Decaff]

I thought the answer was 78.

[CPallini]

42. :-D

"In testa che avete, Signor di Ceprano?" -- Rigoletto

[Greg Utas]

Yeah, you're both on the AR page. :-D

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The fox knows many things, but the hedgehog knows one big thing.