Mental calculation

BogdanovBelsky_UstnySchet.jpg (108 KB)

“the looks on the faces of the students in this 1895 painting by n. bogdanov-belsky are wonderful. i love moments when everyone is really focused on trying to figure something out. they are counting in their heads and feeling hopeful and confident that they can solve the puzzle shown on the board if they just think a little more…

(10^2 + 11^2 + 12^2 + 13^2 + 14^2) / 365

try it – no calculating aids allowed!”
amandabauer.blogspot.com/2010/02/mental-calculation.html


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    nyokkiMaxwell Edisonskat1140NoOneInParticularbytehead Recent comment authors
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    #makecasemdsgreatagain
    Member

    Is it 27?

    #makecasemdsgreatagain
    Member

    I meant 47, is this going to make me fail in life?

    dieAntagonista
    Guest

    No because you didn’t even try, you’re just trying to make yourself look silly like with all the racist comments you make.

    #makecasemdsgreatagain
    Member

    But…but…stupid jew.(Runs off crying.)

    dieAntagonista
    Guest

    I love this. Amazing find, Atk. I have never heard of this painter before and he’s already in my top 10.

    natedog
    Member

    2 1/2?

    Tricknology
    Member

    42.

    Awesome1
    Member

    Why must you stare so intently at me always

    nyoki
    Member

    Sorry dude, can’t help it.

    NoOneInParticular
    Member

    Took me about two minutes to work it out entirely in my head – no paper, no calculator, no cheating. It’s not really that hard. The only thing “hard” about it is remembering the previous numbers when you go to add them up. Each individual calculation is pretty simple. Most folks had to memorize the times table through to 12 as kids, and 13*13 and 14*14 is easy enough to do in your head. It’s even easier to do in your head as the partial sums of the top turn into a number (trying not to give too much away… Read more »

    Halon50
    Member

    I hate your face.

    Halon50
    Member

    Meant jokingly, of course. Still hate you though. (‘~’)

    NoOneInParticular
    Member

    One of these days, I’ll actually set a real avatar for my account. 🙂

    TGGeko
    Member

    Ah, see I just worked it out long hand on paper. Took me about 2 minutes. I’ve never been one for mental calculations.

    MonkeyHitman
    Member

    haha you said aids lol

    Puulaahi
    Member

    Oh how the times have changed. Laziness due to technology. Dumbing down down down.

    Maxwell Edison
    Member

    I worked it out in my head, but it took me a minute. When I noticed that 13^2 + 14^2 was 365, I added up the first three. So I got 2. Mostly my big hangup was not knowing offhand what 14^2 was so I had to do that, and I kept getting distracted thinking about sex.

    Paul_Is_Drunk
    Member

    The answer is 2.

    It just takes remembering what numbers are times themselves (or more correctly, to the second power) then adding them up. Sadly, I thought it was going to be something/365, even after realizing the first three number equaled 365. Never memorized 13^2 or 14^2, so I had to do them in my head quickly.

    Professor Ratbaggy
    Member

    Took about half a minute in the head.  It’s 2.

    Brushaway
    Member

    took me more like 5 minutes 🙂
    is there a clever way to do this? i guess the point of the exercise is keeping your mind organized enough to calculate, store, and sort at the same time. today, we learn to use aids to do the first 2. this makes the sorting process less “conscious”, i.e just plugging in the different numbers different places and see if we get something that looks like the kind of answer maths tasks generally have…like…2?
    great post atk

    Maxwell Edison
    Member

    The trick is to add them as you go and then realize that once you’ve gotten halfway through it, you’ve got 365, and then hypothesize that the other half will also equal 365 so you get a nice pat answer like 2 out of that long pile of goop, and then test the hypothesis, be satisfied by the result, and publish. SCIENCE!

    mikoyangurevich15
    Member

    The question should be why mathematics are being taught to dirt poor Russian peasants .

    Troik
    Member

    I liked that a lot, and I really stumbled over the answer more then I really calculated it. I added 10²; 11² and 12² together in my head, since the result was easy enough to remember I started anew with 13² and 14² and noticed the results was the same as for the previous three, so the answer was easy enough…but yah, took me a couple of minutes.

    nyoki
    Member

    I guesstimated. I figured the answer was a whole number, evenly divisible by 365. Not hard to figure 365*2=730 and 365*3=1095, so I guessed 2. Working w/ 365 is pretty easy since we work w/ 360 for so many daily things.
    Prolly about a minute of think time, tops.

    Dreth
    Member

    man fuk math u aint nevr guna use dat shit in rel life yo

    Troik
    Member

    There is of course a simpler way you could do this much more quickly, which I actually use a lot. By simple assuming that the answer wouldn’t be anything like 3,7575397 and that it’s very likely that the number is an integer, you can guess your way through this. Everybody knows that 10² (or 10*10) is 100 and most people know that 15*15 is 225, so you can kinda assume that all results will be in the ballpark between 100 and 200, if you roughly estimate the average to be around 150 and simple take that 5 times (for each… Read more »

    bytehead
    Member

    I used Excel, and still got the wrong number.

    It helps if you use =sum(a1:a5) and not =sum(a1,a5). I knew it was wrong, I just couldn’t figure why it was wrong.

    100110110110010
    Member
    100110110110010

    rearrange it as:
    (x-2)^2 + (x-1)^2 + x^2 + (x+1)^2 + (x+2)^2 / 365
    which simplifies to:
    5x^2 + 10 / 365



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