General Discussion

Donald Ian Rankin

(13,598 posts)

16. I'm a professional mathematician, and this would give me pause as you presented it.

Sat Jun 25, 2016, 07:01 PM

Jun 2016

In the form in the video, it's easy.

But as you've written it in ASCII, it's horribly ambiguous. Brackets Over Divide Multiply Add Subtract, but does a / with a thing on the left and a thing on the right count as an "over" or a "divide"?

If I had to, I would have plumped for the interpretation that matches the video, taken it as an "over", and evaluated the / before the ÷, but I don't think a mathematician would ever write the formula that way - they'd either actually put the 1 over the 3, or put brackets round it for clarity.

The people who *do* regularly write formulae looking like that are computer programmers. In programming languages you typically don't have a ÷, so / is explicitly used as "divide", and you evaluate left-to-right, so 3 ÷ 1/3 would come out to 1, not 9.

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A lot of people are having trouble with this math problem that requires some basic algebra [View all] sarisataka Jun 2016 OP

I don't understand why this is supposed to be hard? scscholar Jun 2016 #1

Quite a few people's algebra never included operator precedence seabeckind Jun 2016 #2

Which is why in my computer programs I just use lots of parentheses. n/t PoliticAverse Jun 2016 #7

Operator precedence Aerows Jun 2016 #23

Very significant in all calculations. BobTheSubgenius Jun 2016 #28

I disagree with the before computers part scscholar Jun 2016 #37

Incorrect. The order of operations has been around since algebraic notation, and probably before Android3.14 Jun 2016 #106

This message was self-deleted by its author Shrike47 Jun 2016 #3

It's a clickbait article oberliner Jun 2016 #5

The statistics are interesting, you have to admit. seabeckind Jun 2016 #9

Click bait articles often provide interesting information oberliner Jun 2016 #14

Dividing by a fraction 1939 Jun 2016 #26

I agree yeoman6987 Jun 2016 #71

It's hard if you don't know that you are suppose to do the division first... PoliticAverse Jun 2016 #6

Because we've forgotten the order of operations! TexasMommaWithAHat Jun 2016 #123

Thanks scscholar Jun 2016 #185

I used to code for actuaries - and made them give me everything with parenthesis hollysmom Jun 2016 #184

I actually got it right. Kingofalldems Jun 2016 #4

I did too, but I think many forget about the order of operations TexasBushwhacker Jun 2016 #169

I might suggest that it's a teacher/education problem seabeckind Jun 2016 #8

Hmmm. I took algebra in the mid-60's. I do not recall SheilaT Jun 2016 #60

As a former high school math teacher teacher educator, you're half right Android3.14 Jun 2016 #113

You didn't forget. seabeckind Jun 2016 #171

My UICSM course was a sort of "New Math", SheilaT Jun 2016 #173

It does not "require some basic algebra". Nye Bevan Jun 2016 #10

+x LongtimeAZDem Jun 2016 #13

lol auntpurl Jun 2016 #25

I am sorry, but you deserved more than one "lol" for this auntpurl Jun 2016 #76

Exactly. Further, you'd seldom run across something like that in real life. Hoyt Jun 2016 #22

I have seen division by a fraction quite often in real life (and you don't always get parenthses) 1939 Jun 2016 #29

Division by fraction, yes. This: 9 – 3 ÷ 1/3 + 1 = ? Not likely. Hoyt Jun 2016 #35

For Christ sakes. Division is the inverse of multiplication and 1 is the multiplicative identity! longship Jun 2016 #77

As written in the OP it is not division by a fraction. Lucky Luciano Jun 2016 #111

I was a nurse and I'm still a weaver Warpy Jun 2016 #151

Could you give me an example of something like 9 – 3 ÷ 1/3 + 1 = ? that you would run into as a Hoyt Jun 2016 #152

I would consider order of operations basic algebra NobodyHere Jun 2016 #68

exactly. it's pre-algebra, if you consider that as math that includes variables. Gabi Hayes Jun 2016 #159

I've seen enough of these to know this: IT DEPENDS UPON WHEN ONE WENT TO SCHOOL. I, for one, WinkyDink Jun 2016 #11

You don't need brackets to solve this! longship Jun 2016 #79

The problem here is the ambiguity. stone space Jun 2016 #83

No fucking need for them. There is no ambiguity here. longship Jun 2016 #86

Some folks insist emphatically that 27/9/3 = 9. stone space Jun 2016 #95

Equivalent operations go from left to right. immoderate Jun 2016 #139

Sorry mate - stone space is correct. Lucky Luciano Jun 2016 #112

I was speaking in general terms of all these alleged "brain-teasers." Get a grip. WinkyDink Jun 2016 #170

Or 4-3. LanternWaste Jun 2016 #175

absolutely correct AntiBank Jun 2016 #183

Ugh. Gormy Cuss Jun 2016 #118

PEMDAS isn't a newfangled thing. n/t lumberjack_jeff Jun 2016 #130

Obviously someone was sleeping during the order of operations lecture Kilgore Jun 2016 #12

Whippersnappers think the way they were taught is somehow superior to 1950's-1970's methods. WinkyDink Jun 2016 #15

That's one I have not come across Kilgore Jun 2016 #18

I'm a professional mathematician, and this would give me pause as you presented it. Donald Ian Rankin Jun 2016 #16

The problem is that 1939 Jun 2016 #30

That is not correct. athena Jun 2016 #49

Yes, / is used inline. Igel Jun 2016 #67

I don't have my Physics textbook anymore, but do have my "Theory of Simple Structures" textbook 1939 Jun 2016 #89

Yup, exactly what I did Godhumor Jun 2016 #34

I hope you use a lot of R or Python for data analysis! Lucky Luciano Jun 2016 #116

This message was self-deleted by its author progree Jun 2016 #44

+ struggle4progress Jun 2016 #54

In programming you always parenthesize so as of avoid future problems. bemildred Jun 2016 #93

Folks may disagree on the value of 3/1/3, but I hope that we can all agree that 3/1/3=27/9/3. stone space Jun 2016 #102

Wouldn't Americans write that as 1/3/3 = 9/27/3? N.T. Donald Ian Rankin Jun 2016 #120

You win! stone space Jun 2016 #126

It's not even algebra, it's basic arithmetic Ex Lurker Jun 2016 #17

Some people probably forget that dividing by 1/3 is the same as multiplying by 3. alarimer Jun 2016 #19

Is dividing by 1/4 the same as multiplying by 4, also? Forgive me, I'm a fine arts major. brush Jun 2016 #40

Yes. n/t PoliticAverse Jun 2016 #48

dividing by the fraction a/b is always the same as multiplying by the fraction b/a JustinL Jun 2016 #74

This message was self-deleted by its author Aerows Jun 2016 #84

Probably forgot "Please Excuse My Dear Aunt Sally". NutmegYankee Jun 2016 #20

BEMDAS is high level math now? whoa. nt Electric Monk Jun 2016 #21

It's poorly written teach1st Jun 2016 #24

You only need parentheses when the order of calculation is different from the usual rule. athena Jun 2016 #27

Thank you! BobTheSubgenius Jun 2016 #32

I'm terrible at math teach1st Jun 2016 #33

This is not a matter of opinion, and it's not just about tests. athena Jun 2016 #43

Here's one teach1st Jun 2016 #45

That says nothing about the rules of math themselves being ambiguous. athena Jun 2016 #47

+1 Person 2713 Jun 2016 #55

I wrote from an elementary teacher's perspective teach1st Jun 2016 #58

Thanks for clarifying. We agree on the fundamentals. athena Jun 2016 #66

Parsing conventions are just conventions, not mathematics. stone space Jun 2016 #82

In that case, you know what is meant from the context. athena Jun 2016 #87

I've always thought that physicists omit c in multiplicative expressions because c=1. stone space Jun 2016 #94

I suspect that the fact that the problem uses two different symbols for notating division... cemaphonic Jun 2016 #172

It depends on how and where you do most of your math Godhumor Jun 2016 #39

Math is math. Excel does not make up the rules of math. athena Jun 2016 #41

Quick, which is the way you'd write this problem using / Godhumor Jun 2016 #42

Again, this is not about Excel. athena Jun 2016 #46

I don't attack people on their math or programming knowledge Godhumor Jun 2016 #50

The question as it is posed in the OP is obviously a math problem athena Jun 2016 #52

You are obviously missing the point that several people in this thread are raising Godhumor Jun 2016 #57

This message was self-deleted by its author athena Jun 2016 #65

Indeed, as far as I can tell "/" is considered an acceptable symbol to denote division Chathamization Jun 2016 #69

Ok I have a phd in math and I disagree with you. Lucky Luciano Jun 2016 #109

My PhD in math tells me that 9 – 3 ÷ 1/3 + 1 = 9 – 27 ÷ 9/3 + 1. stone space Jun 2016 #114

Well they certainly are equal! Just a roundabout way to get there! Lucky Luciano Jun 2016 #117

I think we can all agree on the value of 2^2^2 as well. stone space Jun 2016 #122

Mind blown!!! LOL. nt Lucky Luciano Jun 2016 #124

A person with a PhD in physics, b.a. in math Duppers Jun 2016 #135

I agree with what you wrote except the outer parentheses are not needed. Lucky Luciano Jun 2016 #137

Exactly. Gormy Cuss Jun 2016 #121

1 Stinky The Clown Jun 2016 #31

It's a simple problem LWolf Jun 2016 #36

I got it right. forgotmylogin Jun 2016 #38

I got the right answer, but we learnt it as BOMDAS rather than BODMAS, and where he mentions it, he OnDoutside Jun 2016 #51

To be accurate, PEMDAS could also be PEDMAS, or PEMDSA, or PEDMSA demwing Jun 2016 #174

I took algebra as a high school freshman in 1965-66. 3catwoman3 Jun 2016 #53

We teach PEMDAS. apcalc Jun 2016 #61

The BEDMAS rule is dumb.. it simply causes confusion and errors. DCBob Jun 2016 #56

As several others have already pointed out, SheilaT Jun 2016 #59

No, you don't do it in order when there are no parentheses SickOfTheOnePct Jun 2016 #63

Enter 2 + 4 x 5 on your calculator. You will get 22, not 30, as the result, Nye Bevan Jun 2016 #70

On cheap calculators, you will get 30. Ms. Toad Jun 2016 #72

Where does this require algebra? Recursion Jun 2016 #62

there should be parentheses Enrique Jun 2016 #64

Order of operations. Learn them. backscatter712 Jun 2016 #73

Software developers are the people I'd expect to get it "wrong" most often. Donald Ian Rankin Jun 2016 #91

Who the hell knows? Parentheses are your friends. stone space Jun 2016 #75

Parsing conventions? SickOfTheOnePct Jun 2016 #88

Here's one parsing, which seems perfectly reasonable to me. stone space Jun 2016 #92

If you're really a mathematician SickOfTheOnePct Jun 2016 #96

Which parsing did you choose? I assume that you got either 9 or 1 as an answer. stone space Jun 2016 #97

I chose the only correct method SickOfTheOnePct Jun 2016 #98

So, does that mean that 27/9/3=9? stone space Jun 2016 #99

Wrong again SickOfTheOnePct Jun 2016 #100

If you claim that 3/1/3=3/(1/3)=9, you should also claim that 27/9/3=27/(9/3)=9. stone space Jun 2016 #101

I'm not claiming anything SickOfTheOnePct Jun 2016 #107

Do you agree that 3/1/3=27/9/3? stone space Jun 2016 #108

Sure SickOfTheOnePct Jun 2016 #115

Nope Lucky Luciano Jun 2016 #128

I suggest you go look at the video SickOfTheOnePct Jun 2016 #129

Point is that the equation as written in the OP is Lucky Luciano Jun 2016 #131

It's written exactly the same SickOfTheOnePct Jun 2016 #133

Sigh...you are dead wrong...it is a division operation not Lucky Luciano Jun 2016 #134

And says that 9 is incorrect SickOfTheOnePct Jun 2016 #155

equivalent operations (i.e. division) happen left to right without parentheses Lucky Luciano Jun 2016 #157

Another person who doesn't understand SickOfTheOnePct Jun 2016 #160

I officially give up - you would fail my class. nt Lucky Luciano Jun 2016 #161

You would fail people who got the correct answer - 1? SickOfTheOnePct Jun 2016 #162

Whatever dude. Lucky Luciano Jun 2016 #165

Nailed it... SidDithers Jun 2016 #119

+1, "with improper punctuation" I had to use order of precedence all the time in writing psuedo code uponit7771 Jun 2016 #168

+1, order of precedence semantics uponit7771 Jun 2016 #167

My 9th grade science teacher grilled us on the order of operation. Sam_Fields Jun 2016 #78

This thread absolutely proves DUers will argue about anything auntpurl Jun 2016 #80

Here's how to determine whether it's ambiguous Orrex Jun 2016 #81

I think the confusion comes in because Aerows Jun 2016 #85

Old math, new math, it's all pffffft to me lol Doremus Jun 2016 #90

Translating math to English, it clearly says GreatCaesarsGhost Jun 2016 #103

I am a mathematician, but had to click through to get it right. Lucky Luciano Jun 2016 #104

The factorial of 9 factorial is YUGE. stone space Jun 2016 #141

You talking about Trump's credit card debt? nt Lucky Luciano Jun 2016 #142

Think of it as 1939 Jun 2016 #164

No I get that...but strictly speaking... Lucky Luciano Jun 2016 #166

4th grade arithmetic Android3.14 Jun 2016 #105

An ambiguous question leads to different answers... SidDithers Jun 2016 #110

Yes KentuckyWoman Jun 2016 #146

It's a simple order of operations peoblem. Adrahil Jun 2016 #125

Clearly, some here are in need of some remedial mathematics: LongtimeAZDem Jun 2016 #127

I googled this edhopper Jun 2016 #132

Dividing by a fraction is the same as multiplying by its reciprocal. backscatter712 Jun 2016 #136

I know that edhopper Jun 2016 #140

That's a keyboarding issue demwing Jun 2016 #178

That's because the Google algorithm failed to recognize that the obelus indicated that the fraction LongtimeAZDem Jun 2016 #181

Just like Donald Trump, I have the best answer. The GREATEST answer! Binkie The Clown Jun 2016 #138

This message was self-deleted by its author stopbush Jun 2016 #143

Well, if you can't do basic math.... Adrahil Jun 2016 #148

This message was self-deleted by its author stopbush Jun 2016 #149

I'd disagree.... Adrahil Jun 2016 #150

This message was self-deleted by its author stopbush Jun 2016 #156

The answer is 42. nt Buns_of_Fire Jun 2016 #144

Wrong equation demwing Jun 2016 #180

I thought the answer was 1... TheDebbieDee Jun 2016 #145

This doesn't come as a surprise, honestly IgelJames4 Jun 2016 #147

Spoiler: applegrove Jun 2016 #153

I was told there would be no math. DemFromPittsburgh Jun 2016 #154

+1 for the SNL reference (nt) LongtimeAZDem Jun 2016 #179

Meanwhile, on DU I'm betting about 10% got it correct. L. Coyote Jun 2016 #158

Now test everyone with some boolean logic rickford66 Jun 2016 #163

Logic 2: Electric Boolean Orrex Jun 2016 #176

It's called parentheses, people. Warpy Jun 2016 #177

why is this ultra simple problem so hard for so many people? AntiBank Jun 2016 #182