Find the remainder when 123321 is divided by 5.
Correct Answer: Option D
The remainder when 123 is divided by 5 is 3.
⇒ So, The remainder when 123321 is divided by 5 would be same as when 3321 is divided by 5.
Now, the remainder when 31 is divided by 5 = 3,
⇒ The remainder when 32 is divided by 5 = 4,
⇒ The remainder when 33 is divided by 5 = 2,
⇒ The remainder when 34 is divided by 5 = 1,
⇒ The remainder when 35 is divided by 5 = 3,
So, the cycle period is 4, since at 34 we get the remainder 1 (after which the cycle starts repeating)
Thus, the remainder when 3321 is divided by is 3 since get the remainder 1 when 321 is divided by 4 (the cycle period).
Or \(Remainder\ in\ {{{{123}^{321}}} \over 5} = Remainder\ in\ {{{3^{321}}} \over 5} = Remander\ in\ {{{3^{320}} \times {3^1}} \over 5}\)
\(= Remainder\ in\ {{{{\left( {{3^4}} \right)}^{80}} \times {3^1}} \over 5} = Remainder\ in\ {{{3^1}} \over 5}\)
= Remainder is 3.
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