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

1. ### Miss ChickenLittle three legged cat with attitudeAdmiral

Joined:
Jul 23, 2001
Location:
Howrah, Hobart, Tasmania
This question is going around Twitter with many different answers so I though I would ask here

Myself I did it this way

8 + 7 = 15
40 + 20 = 60
60 + 15 = 75

Joined:
Jan 27, 2011
Location:
The Backwoods
48
+27
_____
75

3. ### StarCruiserFleet CaptainFleet Captain

Joined:
Dec 26, 2002
Location:
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 ChickenLittle three legged cat with attitudeAdmiral

Joined:
Jul 23, 2001
Location:
Howrah, Hobart, Tasmania
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

Joined:
Feb 7, 2006
Location:
auntiehill
This way. But, sadly, I still actually say the words "carry the one" in my head.

6. ### Miss ChickenLittle three legged cat with attitudeAdmiral

Joined:
Jul 23, 2001
Location:
Howrah, Hobart, Tasmania
yes, adding from right to left and carrying the 1 was another way people explained how they did it.

Joined:
Jan 27, 2011
Location:
The Backwoods
I did that same thing.

Velocity, Miss Chicken and Avro Arrow like this.

Joined:
May 1, 2011
Location:
milky way, outer spiral arm, Sol 3
yep. That's the way I do it

9. ### MykoFleet CaptainFleet Captain

Joined:
Sep 15, 2004
Location:
Stockholm, Sweden
I would do 48 + 20 = 68, then add the 7.

Spot's Meow and Miss Chicken like this.

Joined:
Aug 21, 2011
Location:
The Black Country, England
50+30=80, then 80-2-3=75

Or

40+20=60
8+7=15
60+15=75

Miss Chicken likes this.

Joined:
Jan 20, 2007
Location:
inside teacake
40 + 20 = 60
8 + 7 = 15
60 +15 = 75

Relayer1 likes this.

Joined:
Jan 7, 2001
Location:
On the run.
My head maths is crap...I did it by rounding up. 50 plus 30, minus 5.

13. ### Miss ChickenLittle three legged cat with attitudeAdmiral

Joined:
Jul 23, 2001
Location:
Howrah, Hobart, Tasmania
I use the following method for multiplying in my head. I am not very good at explaining it but I hope this makes sense

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. ### MykoFleet CaptainFleet Captain

Joined:
Sep 15, 2004
Location:
Stockholm, Sweden
Sometimes I just wait the 30 seconds until Rachel Riley gives me the answer.

Jono likes this.

Joined:
Nov 20, 2012
Location:
JirinPanthosa
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.

Joined:
Oct 4, 2003
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.

Joined:
Jul 31, 2001
Location:
My mansion on Qo'noS
48+20+2+5

Kor

Spot's Meow likes this.

Joined:
Jul 4, 2008
Location:
There
That's the way I'd do it.

Joined:
Jul 1, 2004
Location:
Hotel California
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.