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What are the last three digits of the number 7^411? How would I go about solving this? Thanks!

Guest Feb 27, 2015

Best Answer 

 #1
avatar+92429 
+10

Note that 7^11 ends in 743

And 7^100  ends in 001

And 7^200 ends in 001 because we would be multiplying (7^100) x (7^100) which would have the following result in the last 3 digits......

       ........001

x     ........001

-----------------

     ..........001

     ........ 00

     .........0

----------------

.............001

 

So.....7^400 would also end in 001 because we would be squaring 7^200 = (.......001) x (........001)   which would have the same three ending digits as above

 

Therefore  7^411 = 7^200 x 7^200 x  7^11   would end in

.................001

.................743

------------------

         .........003

         .........04

         .........7

--------------------

.................743

 

And 743 is the answer.....!!!

 

CPhill  Feb 27, 2015
 #1
avatar+92429 
+10
Best Answer

Note that 7^11 ends in 743

And 7^100  ends in 001

And 7^200 ends in 001 because we would be multiplying (7^100) x (7^100) which would have the following result in the last 3 digits......

       ........001

x     ........001

-----------------

     ..........001

     ........ 00

     .........0

----------------

.............001

 

So.....7^400 would also end in 001 because we would be squaring 7^200 = (.......001) x (........001)   which would have the same three ending digits as above

 

Therefore  7^411 = 7^200 x 7^200 x  7^11   would end in

.................001

.................743

------------------

         .........003

         .........04

         .........7

--------------------

.................743

 

And 743 is the answer.....!!!

 

CPhill  Feb 27, 2015
 #2
avatar+94088 
0

I like these - thanks Chris. 

Melody  Feb 27, 2015

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