Do you do simple math "out loud" in your head?

[LostAngeles]

I actually visualize the numbers sort of. My method of mental addition is simply a matter of breaking things down. Like if you asked me to add 57 and 86, I would pull 3 from the 86 and give it the 57 to make 60 and 83 and then getting 143. Multiplication takes a bit more work. If I can factor things and use powers that I know, it makes things a little easier. What makes things even easier is if I can see the numbers with my own eyes.

This used to impress people when I worked at the arcade and had to calculate how many tickets they had and how much they had used up.

 

[TeaBag420]

I still do some simple math out loud. I find that I can often catch and correct errors that way, and can get a better feeling of whether a result makes sense.

When I was a teenager, I worked at McDonald's, in an age when the cash registers did not add up the tab for you.

I'm surprised no one has called you on this. When did cash registers not add up the purchase? What did they do instead? I'm calling "made-up story" on this one.

 

[Skeptical Greg]

I'm surprised no one has called you on this. When did cash registers not add up the purchase? What did they do instead? I'm calling "made-up story" on this one.

Uhhh.. Did school let out early today?

Believe it or not, there was a time ( only about ~ 25 or so years ago), when order takers at restaurants did not use a cash register to take orders. They wrote them on paper.. They may have been entered into a register later by a manager..



Get a life..

 

[TillEulenspiegel]

OH Brain flash!!!!

Brian mentiond the dot's he learned at school. As A child I played with LEGO constantly, I think the Bars I visulise might actualy be an abstract of the side of a LEGO brick. I will have been trying to get the lenght of my walls right and ration my bricks about the same time as I was lerning how to do addition.

O.

That's both funny and telling, the "idealized" method of "thinking" about abstracts is if you can organize the problem as a sight/sound/smell response You jump past the drugery of linear / rational thinking .

People who do very difficult mathematics seem to use the term "Visualize". Now that sounds really strange but it is true. Many geniuses see the problem as a kind of recognizable scenario and respond not to the abstract (1-2= bla) but a kind of ..shoot I don't know " picture" for want of a better word. I do that when I hear and play music , I know thats it's not a linear construct like theory would be. I Know about 0 theory but what I play is not mimicry but individual ( influenced of course) That is the Ghost in our machine.

 

[Brian]

I actually visualize the numbers sort of. My method of mental addition is simply a matter of breaking things down. Like if you asked me to add 57 and 86, I would pull 3 from the 86 and give it the 57 to make 60 and 83 and then getting 143. Multiplication takes a bit more work. If I can factor things and use powers that I know, it makes things a little easier. What makes things even easier is if I can see the numbers with my own eyes.

This used to impress people when I worked at the arcade and had to calculate how many tickets they had and how much they had used up.

I do that too. If I need to add 63+34, I take the 3 and 4 and get 7. Then I add 60+30=90+7=97

 

[Brown]

Believe it or not, there was a time ( only about ~ 25 or so years ago), when order takers at restaurants did not use a cash register to take orders. They wrote them on paper.. They may have been entered into a register later by a manager..

The cash registers we used were not adding machines. All they did was keep track of how much money was supposed to be in the drawers. If you rang up $1.50, for example, you had to conclude the transaction (after making change, if necessary) by having $1.50 more in the drawer than was there before the transaction. Overrings (when you rang up too much) and refunds were a hassle, and had to be handled by a manager.

 

[The idea]

[...] when I add 5 to 7, I start counting from 7 until I reach 12 (or whatever the result is). At the age of 49 I still cannot add two single-digit numbers without counting.

Try using this method.
We want to introduce the number 10.
So we replace 7 with 10-3
We get 5+10-3
Now subtract the 3 from the 5
(because that's easy to do and we want to keep the 10).
We get 2+10

You just have to remember this set:
{ {1,9}, {2,8}, {3,7}, {4,6}, {5} }
This allows you to compute 10-n for any single-digit number n.

 

[Soapy Sam]

C/F conversion is so simple! Amaze your friends! Draw graphs on napkins.
Memorise these number pairs
212 100
32 0
-40 -40

The rest is geometry!

That will be $5.00

Next week we will explain how to calculate PI with a coke can and a bit of string.

 

[TeaBag420]

Uhhh.. Did school let out early today?

Believe it or not, there was a time ( only about ~ 25 or so years ago), when order takers at restaurants did not use a cash register to take orders. They wrote them on paper.. They may have been entered into a register later by a manager..



Get a life..

He said the cash register didn't add up the purchase, not that he didn't have a cash register. You sound like you may have issues. "Believe it or not" when I used to go to McDonald's back in the 1960's, they used cash registers. In a previous incarnation, this is where I would tell you to blow me, but I don't do that anymore.

I don't understand why you're asking about when school let out. Do you by any chance have a state-mandated sign in your front yard?

 

[TeaBag420]

The cash registers we used were not adding machines. All they did was keep track of how much money was supposed to be in the drawers. If you rang up $1.50, for example, you had to conclude the transaction (after making change, if necessary) by having $1.50 more in the drawer than was there before the transaction. Overrings (when you rang up too much) and refunds were a hassle, and had to be handled by a manager.

And they kept track of how much money was supposed to be in the drawers by doing what, exactly? I mean, without addition. You seem to be saying that McDonald's in the mid-twentieth century chose not to avail itself of 1920's technology. This should be interesting. Unless you'd care to fold now.

 

[Carn]

To all the fahrenheit to celsius calculation problems:

Don't you think it would be time to finally give in?
For the sake of your children and grandchildren?
Wouldn't that be worth to forget those strange units, they no longer having to learn that calculation?

Carn

 

[Brian the Snail]

Re: Re: Re: Re: Do you do simple math "out loud" in your head?

Sure thing. I break the formula down this way:

F = 9/5C + 32

9/5 is 1/5 shy of 2, so the first move is to simply double C. To which 32 can be added quickly. The final trick is to recognize that 1/5 is 2/10. 10ths can be handled quickly, because that's just a decimal shift, right? So, put it all together:

double C, add 32, subtract 2/10s:

100C -> 200F-> 232F-> 212F

That's actually quite nifty- I'll have to remember that one. I wonder if there's an equally simple way to go from Fahrenheit to Celsius (though I somehow doubt it, since 5/9 is a lot nastier than 9/5).

In a similar, but infinitely less useful, vein, when I was younger and sadder I had a kind of party trick where I could quickly square any two-digit number. It's actually a pretty simple thing to do if you remember the expansion (x+y)<SUP>2</SUP>=x<SUP>2</SUP>+2xy+y<SUP>2</SUP>. Then, if you have, say the number 53 to square, then just take 50<SUP>2</SUP>=2500, 3<SUP>2</SUP>=9, and 50*3*2=300, and add them all up 53<SUP>2</SUP>=2809. You can also do the same thing using subtraction, which is useful if the second digit is large (for example, the number 49). It can actually look quite impressive if you're quick, which just needs a bit of practice, especially if you're good at mental arithmetic and can hold a few numbers in your head.

 

[BillHoyt]

Uhhh.. Did school let out early today?

Believe it or not, there was a time ( only about ~ 25 or so years ago), when order takers at restaurants did not use a cash register to take orders. They wrote them on paper.. They may have been entered into a register later by a manager..



Get a life..

Diogenes,

If you want to drive crazy those who've grown up never knowing cash registers that didn't calculate, try the .25 trick. If your total is anywhere between .76 and .99, give them the change that will force them to return a quarter. Most cashiers will just look at it kind of funny, key in the amount and do what the calculator says. But the fun ones are very certain you don't know what you're doing and often end up arguing that you've given them too much. This is especially fun when the systems are down or busy and they are forced to have to think about making change.

Examples: $ 4.91 tab, give him $ 5.16 or $ 3.76 tab, give her 4.01

To play this game quickly, I think how far off the tab's required coinage is from .75. (.91 for instance is 16 away, so 5.16 is what I should give)

I find this one almost as funny as Randi's "spray the $20 bills with starch" trick to mess up cashiers equipped with those stupid counterfeit detection pens. Although I still think he should spray the starch through a stencil that says "nitwit".

 

[Skeptical Greg]

He said the cash register didn't add up the purchase, not that he didn't have a cash register. You sound like you may have issues. "Believe it or not" when I used to go to McDonald's back in the 1960's, they used cash registers.

No one said they didn't use registers.. Brown said:

"... when the cash registers did not add up the tab for you.. "

Some of us knew exactly what he was talking about, some didn't care and at least one of us got all excited because they thought they had dicovered a big boo-boo, and had nothing else to add to the discussion..

In a previous incarnation, this is where I would tell you to blow me, but I don't do that anymore.

Don't try to act grown up on my account. I promise not to tell.

I don't understand why you're asking about when school let out. Do you by any chance have a state-mandated sign in your front yard?

I have no idea what you are talking about, but I will certainly defer to what I trust is your expertise in this regard..

 

[wollery]

I don't have to do addition out loud in my head unless both numbers are 4 figures or more, and I don't have to do multiplication out loud unless it's higher than 12x12. I do subtraction out loud if the numbers are more than 3 figures, and I have to do division out loud unless the denominator is 2, 5 or 10, or the sum is obvious (eg 81/3).

As for the cash till thing, I used to work the bar in my hall of residence, and the till there didn't add up the prices for you. At least, if it did no-one ever showed me. But then, I never needed it to, so I wasn't bothered.

 

[MESchlum]

Re: Re: Re: Re: Re: Do you do simple math "out loud" in your head?

That's actually quite nifty- I'll have to remember that one. I wonder if there's an equally simple way to go from Fahrenheit to Celsius (though I somehow doubt it, since 5/9 is a lot nastier than 9/5).

That's where my method works well.

C = 5/9 (F - 32)

Compute F - 32

Halve the total, and call it X.

Compute X + 10% of X, and you're pretty much there.


Why?

5/9 = .5555555...

So = .5 + 10% of .5 + 10% of 10% of .5....

If you want an exact value, you'll usually end up with a fraction, which can be quickly evaluated once you know the first terms (there are shortcuts here, but practice is the best way to pick them up).

Example: 100 F

100 - 32 = 68

68/2 = 34

34 + 3.4 = 37.4

37.4 + .34 = 37.74

The answer is 37.77777....

 

[TeaBag420]

Originally posted by TeaBag420
He said the cash register didn't add up the purchase, not that he didn't have a cash register. You sound like you may have issues. "Believe it or not" when I used to go to McDonald's back in the 1960's, they used cash registers.

No one said they didn't use registers..

I was responding to a statement that clearly said registers were not used in SOME restaurants. I brought the argument back to McDonald's, which was the restaurant originally under discussion.

Brown said:

"... when the cash registers did not add up the tab for you.. "

Some of us knew exactly what he was talking about, some didn't care and at least one of us got all excited because they thought they had dicovered a big boo-boo, and had nothing else to add to the discussion..

See above; I have read the discussion accurately, you have not.

Don't try to act grown up on my account. I promise not to tell.

I'm not falling for that one again, Father.

 

[Brown]

Some of us knew exactly what he was talking about, some didn't care and at least one of us got all excited because they thought they had dicovered a big boo-boo, and had nothing else to add to the discussion..

I do not waste my time reading posts of those who deliberately pretend to be dense, or who are actually very dense and are trying to provoke a reaction. Nor do I waste my time with blowhards or nuts. The one who "got all excited" is one of those who does not deserve any attention. I am content that there are those out there who know what I was talking about, and leave it at that.

 

[Skeptical Greg]

I was responding to a statement that clearly said registers were not used in SOME restaurants. I brought the argument back to McDonald's, which was the restaurant originally under discussion.

Where do you get

" ... a statement that clearly said registers were not used in SOME restaurants. "

out of

" ... the cash registers did not add up the tab for you. " ?

No one misunderstood this except you.

After having wet yourself, thinking you had caught Brown making up a story, you are furiously backpedaling, hoping no one will notice..

Since you feel " last word = win ", go for it, and congratulations in advance..



P.S.

Psssst . Brown, I know you are above this and don't need defending, I just don't have anything better to do right now..

 

[LostAngeles]

I do that too. If I need to add 63+34, I take the 3 and 4 and get 7. Then I add 60+30=90+7=97

Uh, no offense, but actually that's how we were taught to add in school. Add the ones, then the tens, etc. etc. What I was doing was making one of the numbers end in 0 and then going from there.