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Yaneev thinks of a number  He subtracts three from the number, then doubles it. Then he subtracts three again, and doubles the number again. The result is his original number  What is ?

 Sep 11, 2021
 #1
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The answer is 22.

 Sep 11, 2021
 #3
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You don't say.  Prove it. 

Guest Sep 12, 2021
 #2
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Yaneev thinks of a number  He subtracts three from the number, then doubles it. Then he subtracts three again, and doubles the number again. The result is his original number  What is ?     

 

Let X represent the original number.  

 

X  =  {[(X – 3) • 2] – 3} • 2  

 

Let me see if I can multiply that out without getting lost.  One step at a time.  

 

X  =  [(2X – 6) – 3] • 2  

 

X  =  4X – 12 – 6  

 

3X  =  18  

 

X  =  6   

 

check answer:  

 

6 minus 3 is three.  3 doubled is 6.  6 minus 3 is 3.  3 doubled is 6.  Looks correct.     

.

 Sep 12, 2021

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