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Question :

If 10^68 is divided by 13 , the remainder is

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Option B is the correct answer.

Explanatory Answer

Question:
If 10^68 is divided by 13, what is the remainder?

Solution:

We calculate remainders of powers of 10 modulo 13:

10^1 mod 13 = 10  
10^2 mod 13 = 9  
10^3 mod 13 = 12  
10^4 mod 13 = 3  
10^5 mod 13 = 4  
10^6 mod 13 = 1  

So, after every power of 6, the remainders repeat in a cycle: {10, 9, 12, 3, 4, 1}.

Now, 68 ÷ 6 = 11 remainder 2.  
Thus, 10^68 mod 13 corresponds to the 2nd element in the cycle, which is 9.

Answer: 9

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