Adding in your head

Discussion in 'Miscellaneous' started by Miss Chicken, Jul 3, 2019.

  1. Miss Chicken

    Miss Chicken Little three legged cat with attitude Admiral

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    This question is going around Twitter with many different answers so I though I would ask here

    How do you add up 48 + 27 in your head.

    Myself I did it this way

    8 + 7 = 15
    40 + 20 = 60
    60 + 15 = 75
     
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  2. Pondwater

    Pondwater Vice Admiral Admiral

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    48
    +27
    _____
    75
     
  3. StarCruiser

    StarCruiser Fleet Captain Fleet Captain

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    Houston, we have a problem...
    Breaking it into manageable chunks is always a good way to handle odd numbers...

    I've done that with percentages (to a point, of course).
     
  4. Miss Chicken

    Miss Chicken Little three legged cat with attitude Admiral

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    Other people said they rounded up, for example one way mentioned was

    50 + 27 = 77
    and then subtracted what they had rounded up by
    77 - 2 = 75
     
  5. auntiehill

    auntiehill The Blueness Premium Member

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    This way. But, sadly, I still actually say the words "carry the one" in my head. :D
     
  6. Miss Chicken

    Miss Chicken Little three legged cat with attitude Admiral

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    yes, adding from right to left and carrying the 1 was another way people explained how they did it.
     
  7. Pondwater

    Pondwater Vice Admiral Admiral

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    I did that same thing. :lol:
     
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  8. rhubarbodendron

    rhubarbodendron Rear Admiral Rear Admiral

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    yep. That's the way I do it
     
  9. Myko

    Myko Fleet Captain Fleet Captain

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    I would do 48 + 20 = 68, then add the 7.
     
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  10. Relayer1

    Relayer1 Vice Admiral Admiral

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    50+30=80, then 80-2-3=75

    Or

    40+20=60
    8+7=15
    60+15=75
     
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  11. teacake

    teacake Fleet Admiral Admiral

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    40 + 20 = 60
    8 + 7 = 15
    60 +15 = 75
     
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  12. Tosk

    Tosk Vice Admiral Admiral

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    My head maths is crap...I did it by rounding up. 50 plus 30, minus 5.
     
  13. Miss Chicken

    Miss Chicken Little three legged cat with attitude Admiral

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    I use the following method for multiplying in my head. I am not very good at explaining it but I hope this makes sense

    [​IMG]

    Though now I only use this method for multiplying a 2 digit number by another 2 digit number when I was younger I could do it with larger numbers.
     
  14. Myko

    Myko Fleet Captain Fleet Captain

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    Sometimes I just wait the 30 seconds until Rachel Riley gives me the answer.
     
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  15. JirinPanthosa

    JirinPanthosa Vice Admiral Admiral

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    For that question my thought process was 50 + 27 - 2.

    For multiplication of two digit numbers my thought process is difference of squares. That is (a - b)(a + b) = a^2 - b^2.

    I learned a trick on Square One when I was 7 that you can square numbers ending in 5 by doing n times n + 1 then tacking on a 25.

    So, say 38 times 74. 56 + 18 times 56 - 18. 55 squared = 3025, plus 55 * 2 + 1 = 3136, minus 18 squared (324) = 2812.

    When I’m doing arithmetic in my head as opposed to on paper I use shortcut heuristics.
     
  16. Silvercrest

    Silvercrest Rear Admiral Rear Admiral

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    Well, that's just cheating!

    For me it's
    48 + 7 = 55
    55 + 20 = 75

    I think sometimes I'd break it up as
    48 + 20 = 68 and 68 + 7 = 75, but I'm not sure.
     
  17. Kor

    Kor Admiral Admiral

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    48+20+2+5

    Kor
     
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  18. John Clark

    John Clark Rear Admiral Rear Admiral

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    That's the way I'd do it.
     
  19. Spot's Meow

    Spot's Meow Vice Admiral Premium Member

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    Same for me, 48 + 20 = 68, then I add on 7 (using my fingers of course).

    This is pretty much how I add most numbers, take the original number and then make the second number a nice round one, on a ten or a 5, then tack on whatever is left over.
     
  20. RandyS

    RandyS Vice Admiral Admiral

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    My math is crap period. They say the old joke is 1+1=11, but to me, that's no joke. 2 1's together makes 11.

    Ironically math is the one subject in school where I got consistent grades. Straight F's every time I took the class.
     
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