Coffeehouse Thread
17 postsForum Read Only
This forum has been made read only by the site admins. No new threads or comments can be added.
Doing calculations with large numbers, in your head?

Hi
I'm to learn to do calculations like 234 * 532 by my head.
I was wondering if anyone here knew a site about how to learn yourself doing this, or got some good tricks, that could help me? 
Chadk wrote:
Hi
I'm to learn to do calculations like 234 * 532 by my head.
I was wondering if anyone here knew a site about how to learn yourself doing this, or got some good tricks, that could help me?
I just do sums like that in my head as you would on paper. It depends on how much time you have whether you can do this or not, but as long as you are quick at arithmatic you will be fine.
Angus Higgins (1st Channel 9 Birthday)

I can do those in my head, but it takes me some time.
I visualise performing the airthmetic in my head the same way you do on paper. It's not that hard really. Although there's probably a better way of doing it. 
W3bbo wrote:I can do those in my head, but it takes me some time.
I visualise performing the airthmetic in my head the same way you do on paper. It's not that hard really. Although there's probably a better way of doing it.
Yeah, the same way as me, it is a similar way to how I memorise Pi Autistic Savants who have a special gift for this type of feat will visualise the numbers as textures, or other images; they can almost sense the answer; I don't think you could learn how to do this though.
Angus Higgins (1st Channel 9 Birthday)

I don't do long maths in my head too well... Not because I can't do the calculations but instead because my short term memory has a life span of about five seconds (compared to the average person's fifteen seconds).
Thus I'd forget the start before I calculate the end. It is a very real problem that is not going away any time soon. And not something you can learn away. 
Manip wrote:
I don't do long maths in my head too well... Not because I can't do the calculations but instead because my short term memory has a life span of about five seconds (compared to the average person's fifteen seconds).
Thus I'd forget the start before I calculate the end. It is a very real problem that is not going away any time soon. And not something you can learn away.
All you need to do is learn where the calculator is and you'll be fine... 
This seems interesting
http://www.virtual.net.au/~bhandley/lua2.htm
(Tried to do it with your example, but it seems you have to round off with the same number... so in your case I'd have to round off both numbers to say 540 ... )
 Keeron 
The Russian Peasant algorithm should be good for this.

Honestly, I use calc.exe in scientific mode. During the 23 hours a day I'm not in front of a computer, I use the calculator built into my cell phone. If that's dead, or I need a quick answer, I estimate for anything involving numbers greater than one digit or more than two operands.

ive always done math backwords / rounding off..
say 174 + 245
id do  100 +200 = 300  then 70(4) + 30 (15)= 400 then 4 +15 = 419 
Rounding is key.
Breaking up large numbers is another strategy.
If you have something like 666 * 50, you can think of it in your head like 6 * 111 * 50
Then it becomes 300 in you head...easy thing to multiply. 300 * 111 is just 300 + 3000 + 30000 (as you would do it on paper....simple to visualize in your head). 
Most profressional abacus (a kind of traditional calculation tools used by Chinese) users can do so, because they have abacus in their head.

I know it's tough for many people, but I never had trouble doing math w/ really large numbers.
1,000,000,000 + 1,000,000,000 = easy for me 
Minh wrote:I know it's tough for many people, but I never had trouble doing math w/ really large numbers.
1,000,000,000 + 1,000,000,000 = easy for me
Okay, smartass... Compute this:
1,234,567,890 * 987,654,321
:in your head. 
SlackmasterK wrote:
Minh wrote:I know it's tough for many people, but I never had trouble doing math w/ really large numbers.
1,000,000,000 + 1,000,000,000 = easy for me
Okay, smartass... Compute this:
1,234,567,890 * 987,654,321
:in your head.
Umm... add the 1, carry the 2, multiply by PI, OK:
1,219,326,311,126,352,690
Am I correct?

keeron wrote:This seems interesting
http://www.virtual.net.au/~bhandley/lua2.htm
(Tried to do it with your example, but it seems you have to round off with the same number... so in your case I'd have to round off both numbers to say 540 ... )
 KeeronI have for years done it in my head rounding or backwards similar jamie and mvpstar.
This is very clever though and I think I have it memorised in under 5 minutes at the site.
Here goes... Pick a sum...
94 x 84 =
6 16 (Round up to 100 and write the difference here)
9416=78 or 846=78
6 x 16 = 96
Answer = 7896
Change the equation to 63 x 48 and it starts to break down quickly... 
Stephen wrote:
Change the equation to 63 x 48 and it starts to break down quickly...
Yeah ain't so smooth anymore but still possible to avoid those big multiplications if your desperate lol.
56*39(5611)/2*100=2250 6*11=2184
63*48
(632) /2*100=3050 13*2=3024
23*77 (can already see the multip. is going to be big, get closer to 50)
*2 /2
46*38½(4611½)/2*100=1725 +4*11½=1771
Conversation locked
This conversation has been locked by the site admins. No new comments can be made.