Question:

If $5^{97}$ is divided by $52$ $,$ then the remainder obtained is

Updated On: Jul 28, 2022
  • $3$
  • $5$
  • $4$
  • $0$
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The Correct Option is B

Solution and Explanation

We know that, $5^{4}=625=52\times 12+1$ $\Rightarrow 5^{4}=52\lambda +1$ , where $\lambda $ is a positive integer. $\Rightarrow \left(5^{4}\right)^{24}=\left(52 \lambda + 1\right)^{24}$ $= \, \_{}^{24}C_{0}\left(52 \lambda \right)^{24}+\_{}^{24}\left(C_{1} \left(52 \lambda \right)^{23} + \_{}^{24}C_{2} \left(52 \lambda \right)^{22}\right)+\ldots +\_{}^{24}\left(C_{23} \left(52 \lambda \right) + \_{}^{24}C_{24}\right)$ (by binomial theorem) $\Rightarrow 5^{96}=52\left[\_{}^{24}C_{0} 52^{23} \lambda ^{24} + \_{}^{24}C_{1} 52^{23} \lambda ^{22} + \ldots + \_{}^{24}C_{23} \lambda \right]+1$ $=\left(a \, m u l t i p l e \, o f \, 52\right)+1$ On multiplying both sides by $5$ , we get $5^{97}=5^{96}\cdot 5=5 \, \left(a \, m u l t i p l e \, o f \, 52\right)+5$ Hence, the required remainder is $5$ .
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Concepts Used:

Binomial Theorem

The binomial theorem formula is used in the expansion of any power of a binomial in the form of a series. The binomial theorem formula is 

Properties of Binomial Theorem

  • The number of coefficients in the binomial expansion of (x + y)n is equal to (n + 1).
  • There are (n+1) terms in the expansion of (x+y)n.
  • The first and the last terms are xn and yn respectively.
  • From the beginning of the expansion, the powers of x, decrease from n up to 0, and the powers of a, increase from 0 up to n.
  • The binomial coefficients in the expansion are arranged in an array, which is called Pascal's triangle. This pattern developed is summed up by the binomial theorem formula.