## [0705] Tough Question

└ posted on Thursday, 30 July 2015, by Novil

**Michael R. Douglas:** This means you’re a little math genius?
**Yuna:** Yeah!
**Michael R. Douglas:** So can I ask you a tough question, then?
**Yuna:** **Yeah!**

**Michael R. Douglas:** A really tough one?
**Yuna:** Yeah!

**Michael R. Douglas:** Okay, what’s 13 x 17 + 3²?

**Yuna:** Something between 100 and 300?
**Ye Thuza:** Yuna isn’t very good in mental arithmetic. Calculating a higher order partial derivative would suit her better.

I got 130 when I did it in my head using my method of breaking it down into parts (10×10 + 3×7 + 3^2) but I forgot to account for the fact that there were two tens being multiplied by one another so according to my calculator I was off by 100. XD At least my method works when I remember details like that.

Yuna should learn to break up those mental calculations, it’s easier 🙂

10×17 = 170

3×17 = 51

3^2 = 9

51+9 = 60

6+ 170 = 230 🙂

Looks like she’s well suited to be a math major. Can’t do simple math, loves complex bits and pieces.

Of course, simple stuff really should just be given to a calculator, anyways.

Don’t worry Yuna, i fried my brain trying to tonit in my head as well.

230

I was able to do it in my head, but if I was only getting the question by ear, I would have taken probably longer than I did.

Come on, Yuna, you can do this! Just remember: “Please Excuse My Dear Aunt Sally”. Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction. Three squared is nine, thirteen times seventeen is two hundred and twenty one, add them together, and you get two hundred and thirty.

I understand he thinks he’s dealing with a little girl.

But a

genuinemathematician wouldn’t even call that question “math”. He wouldn’t ask it.It’s arithmetic. Hardly any overlap between the two.

In fact, with a few notable exceptions (Gauss and vonNeumann came to mind) mathematicians tend to be rather poor at simple arithmetic.

Modern mathematics is all about relationships between objects, and those objects are often quite abstract things. Numbers hardly ever enter into proofs

Suppose I felt (N-1) * (N+1) + 1 = N*N because it works when I test it on every integer N <1000.

Means nothing. It might not be true when N = 1001. There are plenty of theorems which look good based on such tests, yet turn out to be false. It would have taken only a single counter-example to disprove Fermat's Last Theorem. Thanks to mathematics though, we know it's true even without making an infinite number of checks.

Mathematics arithmetic. And Douglas would know that.

I did 13×20 minus 13×3 then added 9. It’s just convenient that 13×3 is only 1 away from a multiple of ten, otherwise I would have gotten totally lost O.o

@ Jeffrey:I seem to recall a few like that. They didn’t care about the actual numerical answer, just the symbolic one.

@ Edda:I wrote “Mathematics is not Arithmetic” and I used the opposite-pointing “<" signs for "not equals"

That was interpreted as an HTML tag and ignored.

I don't want to be mis-understood.

It’s kind of sad how quickly I got the answer 230.

Sad because I know it comes from poker.

230, Yuna be ashamed of yourself, that’s easy as soon as you work out that the last sum isn’t some complex formula thing.

why would he try and test her mental arithmetic rather than her mathematical abilities?

Why aren’t you tutoring Yuna? Though I doubt she’ll be getting schooled by anyone after the next couple strips.

@ Edda:In my head:

7*13=91

3^2=9

17*13+3^2=91+10*13+9=100+130=230

Alternative method two:

13*17+3^2=(15-2)(15+2)+9=(15^2)-(2^2)+9=225-4+9=221+9=230

“We’re not computers, Sebastian.”

This is how I’d do it in my head:

10×10 + 10×3 + 10×7 + 3×7 + 9

100 + 100 + 21 + 9

230

There are a lot of different types of mathematical genius. Some people can perform calculations in their head faster than you could type the question in a calculator, others just need to write down the numbers while solving a long and complex equation.

@ Threadnaught:Not really if you just hear it out loud.

A lot of people struggle to do things mentally, particularly when they’ve not got a reference as to what the question is like we do right in front of us.

For me that would go in one ear and out the other.

did it mentally, took me some times tho, cause ofcourse he used prime numbers didn’t he, he had to XD

took me some time to decide how to go mentally with it without forgetting part of it midway:

3²=9

10*3=30

7*3=21

21+30+9=60

10*17=170

170+60=230

@ Gram91:Ditto

I figured it almost immediately.

I am smarter than a little girl, success!

@ Sgt_flyer:Personally, I set it up this way:

10×17 = 170

3×(10 + 7) = 30 +21 = 51

3^2 = 9

Also, this way is pretty easy as as well:

13*17+3*3=10*17+3*17+3*3=17*10+3*20=170+60=230.

I did this like any normal math problem. Did 17×13 in my head. 3 squared doesn’t need calculation for me 3×3=9. 51+170+9. It took me 30 seconds to a minute to do it in my head, but I imagined it like I was writing it down.

230. … I mean…. She’s not wrong.

Should’ve asked her a REAL stumper, like “Given E=MC^2, solve for Magic.”

@ Edda:I kinda get why he asked that arithmetic problem, you see typically children under the age of 10 are unable to work out multiplication in their heads, I can’t remember the exact reason but it has something to do with their brains having reached a certain stage of development yet.

The middle school teachers got very upset that I could instantly give the exact answer 100% of the time but couldn’t really tell them how or “show my work”.

There was never any work; I just know the answer.

Easy method is saying that since 10×17 is 170, and you have a 3×17 left, the 3×10 portion is 30. This gives 200. you are then left with 3×7 plus 9, which should be easy to figure out as 30 again. Should take all of 15 seconds for most adults who are decent at math. (There are many who are bad at math to the point of hearing odd numbers in there and saying ‘Forget it.’)

Yeah, this isn’t a tough problem, but given Yuna’s age and a weakness to performing the basic mental math functions in her head, I could see her being adept at other things and having problems with this. Also, agreed with Mr. Random that her answer isn’t totally wrong.

As for q’Tzal’s remark: Yeah, I was the same way, and my brother was worse (he gets math at a level that is amazing to me, and he regularly stumped the math teachers with his work… and he had no clue for how to show work either.) The problem is that they are supposed to grade on it, and most of them aren’t math experts… they just got told that they were a math teacher. At least, that’s how it is in the states (which makes me pity them just a little faced with the horror of intelligent students with a talent in a given subject.)

I’m so like that in math! The easy ones, I always get wrong. The hard ones are as easy as 3.14159265359!

@ Tudza

Much quicker way that I was approaching it:

13^2 + 4*10 + 4*3 + 9 = 230

Mostly chosen because I have the squares down pat up to 25. Sounded a lot less convoluted in my head.

Technically, Yuna wasn’t wrong, though!

Once you play a Dream Pod 9 mecha-themed game, and fooled around with the vehicle construction system by making all kinds of of weird concept vehicles, that sort of math becomes second nature. Yuna should stick with Battletech… I mean early-edition Battletech. Or maybe Rogue Space Mechs? =P

I tend to use the difference of two squares for problems like this: (x-c)*(x+c) = x^2 – c^2

So 13*17 = 15^2 – 2^2 = 225 – 4 = 221

Then you just add 9 to get 230.

It might be a bit overkill here, but it can make larger calculations like 47*53 a breeze. 🙂

13 x 17 + 3²

3² = 9

13 x 10 = 130

10 x 7 = 70

3 x 7 = 21

130 + 70 + 21 + 9 = 230

what scares me: I wasn’t really good at mental arithmetic. After I learned to break down the bigger numbers and to imagine the numbers as objects that I can move around, this takes less then 5sec

ok, I am good at math and bad at arithmetic.

first try:

10*10 = 100, 20*20 = 400 so more than 100 and less than 400.

I do not know how Yuna compute 300.

second try (I had already saw the right answer on comments):

10*17 + 3*(17+3) = 170 + 60 = 230.

the better you get at advanced math, the worse you get at basic arithmetic. i think there is an xkcd for that, but couldn’t find it.

also MORE YUNA PLEASE

Damn, when doing it in my head I accidentally added another 13 <_<

Points for the effort! “A higher order partial derivative” is certainly better than mental arithmetic you usually in this context (which I suppose was the joke).

Here’s a relatively tough question:

“Show that any homology sphere which is a surgery on a knot is the boundary of a simply connected 4-manifold.”

Or if you insist on explicitly calculating something:

“Consider S^7 \approx {(q,h)\in\mathbb{H}^{2}}. Let E=S^{7}\times_{SP_1}\mathbb{C} be the obvious vector bundle, thought of as a \mathbb{C}-vector bundle. Calculate \int_{S^4} c_{2}(E), where c_2 is the second Chern class.”

I don’t think I could solve simpler math equations myself without resorting to Google.

Did this mentally:

17+17=34

34+17=51

17+10=170

51-30=21

Therefore: 221

3*3=9

221+9=230

Sgt_flyerwrote:Hey, seems we think alike! Although I finished calculating 13×17 first before adding the 9.

So many ways for a simple thing, huh.

All the comments on mathematics and none on how adorable Yuna is? Very peculiar indeed.

@ Edda:I was gonna mention the same thing, but since you already said it so eloquently, I’m just gonna nod in agreement.

@ Sgt_flyer:She could break it down even further:

7 x 3 = 21

7 x 10 = 70

3 x 10 = 30

30 + 70 = 100

100 + 21 = 121

121 + 9 = 130

@ Edda:Algebraic equations require arithmetic operators. If you dismiss arithmetic as not being part of mathematics you must also dismiss algebra.

I find it ironic that you would dismiss arithmetic as not being part of mathematics on the basis that it involves numbers.

@ DanialArin:Yeah, but break it down too much and you slow yourself down with little problems, can lose your mental place (causing the whole thing to fall apart), etc.

The fastest way I’ve arrived at the right answer is:

10*17 + 3*17 + 3^2

170 + 51 + 9

230

I do love Ye Thuza’s very motherly way of prodding Douglas and trying to butter Yuna up. Cute touch.

I feel so bad for Yuna here.

Rule of thumb: if it’s implemented by a calculator, it doesn’t have much to do with math.