# Thread: O/T: Math. Again (I am trying to learn) :)

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## O/T: Math. Again (I am trying to learn) :)

So it seems I like to work heavy math problems from the end to beginning, backwards.

No, I dont want the answer. But it is easier for me to solve the problem from right to left.

I think I made a multiplication system that also worked backwards.

Say
235,975
X
24,763

And no thank you, I dont do that stuff anymore I am retired

Answer in moments with a pencil and paper. Work the math backwards. Get rid of the heavy stuff and pare down the small numbers.

I thought that is how everyone did long number math. JR

Last edited by JRouche; 07-20-2019 at 02:39 AM.

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I'm not sure what you mean. Multiplication of numbers like you show is performed by going right to left on the multiplicand, and subtotals left-shifted for each power of 10 in the digits of the multiplier. It's probably a good mental exercise to perform such operations by hand, occasionally, but it is rarely needed when you can buy a calculator for less than the cup of coffee you will need to lubricate your brain for manual math.

If you really want to dig deep into the mathematical and computation gymnastics involved in computer programming, read the following:

https://docs.oracle.com/cd/E19957-01..._goldberg.html

For example:
Another grey area concerns the interpretation of parentheses. Due to roundoff errors, the associative laws of algebra do not necessarily hold for floating-point numbers. For example, the expression (x+y)+z has a totally different answer than x+(y+z) when x = 1030, y = -1030 and z = 1 (it is 1 in the former case, 0 in the latter).
There are some shortcuts that can be used sometimes for long number math. For instance:

1,234 x 99 can be simplified as 1,234 X 100 -1,234 = 123,400 - 1,234 = 122,166

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Is it just me? ...or is there a shortage of coherence in this room?

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Perhaps. But I got zig-zags and quit reading.

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The most interesting math I find is geometry and trig in the application of what we do, and throw in some calculus for PID algorithms in motion control. Everything else will bore you to tears.

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6. vpt
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I could never figure out the deal of 'multiplication before everything else' deal. Where you have a string of math equations and somewhere in the middle is a multiplication equation.

Like:

4+5-3/2+5x7-6=

I have it engraved in my head to just work from left to right. But I read you are supposed to start with the multiplication first?

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Originally Posted by lynnl
Is there a shortage of coherence in this room?
No, but there seems to be a shortage of coherence.

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Originally Posted by vpt
I could never figure out the deal of 'multiplication before everything else' deal. Where you have a string of math equations and somewhere in the middle is a multiplication equation.

Like:

4+5-3/2+5x7-6=

I have it engraved in my head to just work from left to right. But I read you are supposed to start with the multiplication first?
4+3*2 = 10

4+3*2 does not equal 7*2 = 14 [ if the desired value was 14 then it would have to be written (4+3)*2 ]

Actually, the rule is;

do what's inside the parentheses first
then
exponentiation
multiplication/division

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Don't remember when I first learned the mnemonic: "My Dear Aunt Sally" - Multiply, Divide, Add, Subtract (i.e. the order of operations). But it was probably before they muddied the water with that exponentiation stuff.

Like Marv's example above shows, it kinda helps to have some sort of agreed upon way of doing things.
Last edited by lynnl; 07-20-2019 at 12:27 PM.

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Khan academy is a wonderful thing. I need to get back into it to exercise my brain. Also watching the video on YouTube of a guy building a simple video card on a breadboard to drive a VGA monitor using logic chips and an eeprom was a life altering experience, "so THAT'S how those analog things are used!"

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