+0  
 
0
1447
6
avatar

Subtract 345 from 678 using the method of complements  (a technique used to subtract one number from another using only addition of positive numbers).

 Jun 18, 2015

Best Answer 

 #1
avatar+33603 
+18

The 9's complement of 678 is 321

 

321 + 345 = 666

 

The 9's complement of 666 is 333 which is the desired result.

 

(i.e. 678 - 345 = 333)

 Jun 18, 2015
 #1
avatar+33603 
+18
Best Answer

The 9's complement of 678 is 321

 

321 + 345 = 666

 

The 9's complement of 666 is 333 which is the desired result.

 

(i.e. 678 - 345 = 333)

Alan Jun 18, 2015
 #2
avatar+118587 
+10

Thanks Alan

It took me ages to work out what you did!

The question is  678-345

NOW    

678+321=999   (1)

345+321=666    (2)

so thinking of this like simultaneous equations using elimination method. 

(1)-(2)

678-345=999-666

678-345=333

 

That is really weird.

Why would anyone want to do that for?

 Jun 18, 2015
 #3
avatar+128061 
0

I have to agree, Melody......I see how  this works, but I don't understand the rationale for wanting to do it.....!!!

 

 

 Jun 18, 2015
 #4
avatar+33603 
+5

This method can be found in computers that use binary arithmetic (where they use 2's complement of course).  

I've never come across 9's complement being used for real in normal base 10 arithmetic though!

.

 Jun 18, 2015
 #5
avatar+128061 
0

Thanks, Alan......that method seemed a little convoluted for everyday practicality......IMHO.....!!!!

 

 

 Jun 18, 2015
 #6
avatar+118587 
0

Thanks Alan :)

 Jun 18, 2015

4 Online Users

avatar
avatar
avatar