a diff reminder qs

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nishit's picture
User offline. Last seen 1 year 29 weeks ago. Offline
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My Question

If N = 1 + 11 + 111 + 1111 + . . . . . . .  11 terms

Then the reminder of N when divided by 12 is

I ‘ll post the answer and diff ways of solvin it after 9pm

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anita1's picture
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I am getting the answer  as

I am getting the answer  as 3

is it correct

shabash_23's picture
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I am not at ease with

I am not at ease with remainder problems but i

tried this in a very crude way.

The remainders of individual terms when divided by 12 are as follows

1 + 11 + 3 + 7 + 11 + 3 + 7 + 11 + 3 + 7 + 11 =  75

when 75 is divided by 12  the remainder is  '3'

pls post any easy and refined way of finding the remainder

thank u

shahid

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kamallohia's picture
User offline. Last seen 2 years 21 weeks ago. Offline
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CRT

Using Chinese Remainder Theorem

12 = 4*3 such that 4*r - 3*t =1, where r =1 and t =1

Let x be the remainder when N is divided by 3 and y be the remainder when N is divided by 4.

So, x = (1-1+0) + (1-1+0) + (1-1+0) + (1-1) = 0

and y = 1 - 1 - 1 - 1 - 1.. = -9 = 3.

S remainder of N when divided by 12 = 4rx - 3ty = 4*1*0 - 3*1*3 = -9 = 3mod12.

Kamal Lohia

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rajesh_6e's picture
User offline. Last seen 2 years 11 weeks ago. Offline
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yet anothr way....

1mod 12=1

10 mod 12=(-2)

nd (10)^n mod 12=4 ,where n>1

there r 11 --1's

   10--10's

n so on

going this way rem=3

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nishit's picture
User offline. Last seen 1 year 29 weeks ago. Offline
Joined: 2007-04-20
Points: 377
Thanks guys. . I can’t

Thanks guys. . I can’t think of any other method. For those who still have not solved the question here is a stepwise explanation

Sum of First two terms is divisible by 12

3 one’s = 111 mod 12 = 3
4 one’s = 1111 mod 12 = (1116 - 5) = (-5) = 7
5 one’s = 11111 mod 12 = (11112 - 1) = (-1) = 11
6 one’s = 111111 mod 12 = (111108 + 3) = 3 = 3
7 one’s = 1111111 mod 12 = (1111116 - 5) = (-5) = 7
8 one’s = 11111111 mod 12 = (11111112 - 1) = (-1) = 11
and the series continues lik this

Reminder of 3rd + 4th + 5th term = 6rd + 7th + 8th term = 9th + 10th + 11th term = 9 = (-3)

So reminder of N = reminder of (9x3) divided by 12 = 3
Modification 2

Reminder of 3 one’s = 3

Reminder of 4 one’s = 7 ( 3 + 4)

Reminder of 5 one’s = 11 (7 + 4)

Reminder of 6 one’s = 15 = 3 (11 + 4)

Reminder of 7 one’s = 7 (3 + 4)

Modification 3

Reminder of 3 one’s = 3

Reminder of 4 one’s = 7 ( 3 + 4)

Reminder of 5 one’s = 11 (7 + 4)

Reminder of 6 one’s = 111000 + 111 = 111   (as 111000 is divisible by both 3 and 4)            
Reminder of 7 one’s = 1110000 + 1111 = 1111   (as 111000 is divisible by both 3 and 4)      
. . . . . .

moral : most of the  reminder qs can be solved in many diff ways . .

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