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Math riddle

 
 
Reply Fri 19 Jan, 2018 01:36 pm
(AB x 2) – 1 = BA
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Type: Question • Score: 0 • Views: 543 • Replies: 12
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fresco
 
  2  
Reply Fri 19 Jan, 2018 04:16 pm
@whimsical,
A=1 B=1
or
A=-1 B=-1
whimsical
 
  2  
Reply Fri 19 Jan, 2018 04:21 pm
@fresco,

thanks
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whimsical
 
  1  
Reply Fri 19 Jan, 2018 04:41 pm
@fresco,
Can there be a solution where A is not the same number as B? Or is that impossible?
centrox
 
  2  
Reply Fri 19 Jan, 2018 05:04 pm
@whimsical,
whimsical wrote:
Can there be a solution where A is not the same number as B? Or is that impossible?

A x B must equal 1. Using integers, A and B must be -1 or +1. However there is an infinite number of solutions, if fractions are allowed,

Code:A=1/2 B=2 A=2 B=1/2
A=1/4 B=4 A=4 B=1/4

etc ad infinitum

all of this form:
A = N, B = 1/N
or
A = 1/N, B = N




ekename
 
  2  
Reply Fri 19 Jan, 2018 08:36 pm
@whimsical,
(AB x 2) – 1 = BA

2 x (10A + B) - 1 = 10B + A

20A + 2B -1 = 10B + A

19A = 8B + 1

B = 7, A = 3

centrox
 
  1  
Reply Sat 20 Jan, 2018 03:35 am
@ekename,
ekename wrote:
B = 7, A = 3


so ((7x3) x 2) -1 = 7x3?

so 41 = 21?
ekename
 
  1  
Reply Sat 20 Jan, 2018 04:52 am
@centrox,
Quote:
(AB x 2) – 1 = BA


When A and B represent single digit integers, AB and BA can be construed to be two digit numbers.

If A = 3 and B = 7 then

37 x 2 -1 = 73
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centrox
 
  1  
Reply Sat 20 Jan, 2018 05:03 am
I was going by the conventional algebra representation I was taught in school, e.g.

https://images2.imgbox.com/9e/8f/odyD3SqP_o.jpg

Where "AB" means "A multiplied by B"

fresco
 
  1  
Reply Sat 20 Jan, 2018 05:58 am
@centrox,
...as was I. But come to think about it there are 'riddles' using letters as place value digits. If I find one I'll post it.
0 Replies
 
whimsical
 
  1  
Reply Sat 20 Jan, 2018 07:41 am
@centrox,
Thanks..
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whimsical
 
  1  
Reply Sat 20 Jan, 2018 07:44 am
@ekename,
Aha cool...
0 Replies
 
fresco
 
  1  
Reply Sat 20 Jan, 2018 09:59 am
@centrox,
....S E N D
+ M O R E
________
M O N E Y

I think these are called 'alphmetic riddlee'. I'm trying thie one noe.
0 Replies
 
 

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