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February 28 2013, 08:41 PM  #1 
Captain
Location: Georgia, USA

Math question
Its talking about negative integers and distributive property. I was following along just fine until I got to this example it asked me to work out. 25x96 Now I thought I had this, so I went about to do this: (25x90) + (25x6) to get my answer but then I read how the book does it and I am completely lost. This is how the book did it: 25x96 = 25 x (1004) = 25x100 + 25 x (4) = 2,500  100 = 2,400 Where did they get this 1004, I realize it equals 96 but what? Can anyone explain to me why it went by 100? What am I missing here?
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"The typical investor would be better off if his stocks had no market quotations at all, for he would be spared the mental anguish caused him by other persons' mistakes of judgement." Benjamin Graham  The Intelligent Investor Chpt 8. 
February 28 2013, 08:44 PM  #2 
Fleet Captain
Location: Space Wales

Re: Math question
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February 28 2013, 08:50 PM  #3 
Vice Admiral

Re: Math question
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February 28 2013, 09:36 PM  #4 
Commodore
Location: milky way, outer spiral arm, Sol 3

Re: Math question
Actually the 1004 makes sense. You can multiply by 100 by simply adding two 0es or shifting the decimal point (or in Europe the decimal comma) two digits to the right. This is a mechanical step that doesn't require much thinking and goes quickly. Then they substract the rest. Imagine their example as: there are 25 boxes with 100 cupcakes each. Someone steals 4 cupcakes from every box. How many are left? See? Now it makes perfect sense (and a belly ache for the thief LOL)
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February 28 2013, 10:39 PM  #5 
Vice Admiral
Location: thestrangequark

Re: Math question
Of course, 96 could also be defined as 90+6 or 8(12), etc. 
February 28 2013, 11:18 PM  #6 
Rear Admiral
Location: Magic realism

Re: Math question
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February 28 2013, 11:24 PM  #7  
Writer

Re: Math question
And that meant that 25 x 96 could also be written as 25 x (4 x 24), and you just move the parentheses and it's (25 x 4) x 24 = 100 x 24 = 2400. It's just an easier and more intuitive route to the solution. So that's two different points where it was possible to get to 100, and that made it much easier to solve those parts. We use base10 mathematics because we have ten fingers, so anytime you can rearrange an equation to get a 10 or 100 or the like in there, it makes it easier to solve.
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March 1 2013, 01:44 AM  #8 
Vice Admiral
Location: thestrangequark

Re: Math question

March 1 2013, 03:33 AM  #9 
Captain
Location: Georgia, USA

Re: Math question
__________________
"The typical investor would be better off if his stocks had no market quotations at all, for he would be spared the mental anguish caused him by other persons' mistakes of judgement." Benjamin Graham  The Intelligent Investor Chpt 8. 
March 1 2013, 03:54 AM  #10 
Vice Admiral
Location: thestrangequark

Re: Math question

March 1 2013, 06:01 AM  #11 
Fleet Admiral
Location: House of Kang, now with ridges

Re: Math question
My math score was so low on my SATs, I think they had to go negative.
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March 1 2013, 11:16 AM  #12  
Rear Admiral

Re: Math question
This is very true. There are lots of "tricks" you can use  like knowing the digits of anything divisible by 3 will, themselves, sum up to something divisible by 3. For example: 1386486 Sum the digits: 36. Sum the digits again: 9. So it's divisible by 3. Similarly anything divisible by 9 can have its digits added up to something divisible by 9. (So 1386486 above is divisible by 9.) You learn them mostly through experience, but also sometimes through being taught them. 

March 1 2013, 12:48 PM  #13 
Admiral
Location: Rhode Island, USA

Re: Math question
Breaking it into 90 and 6 doesn't help...
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March 1 2013, 01:39 PM  #14 
Rear Admiral
Location: Magic realism

Re: Math question
__________________
"Sans le canard de Vaucanson vous n'auriez rien qui fit ressouvenir de la gloire de la France."  Voltaire  Flip flap! 
March 1 2013, 02:11 PM  #15 
Vice Admiral
Location: Massachusetts

Re: Math question
Also, buy a calculator. 
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