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    Question

    Find remainder when 7¹⁰⁰ is divided by

    100.
    A 1 Correct Answer Incorrect Answer
    C 2 Correct Answer Incorrect Answer
    D 5 Correct Answer Incorrect Answer

    Solution

    ATQ,

    By Euler’s theorem, ϕ(100)=40 ⇒ 7⁴⁰ ≡ 1 mod 100. 100=40×2+20 ⇒ 7¹⁰⁰ ≡ (7⁴⁰)²×7²⁰ ≡ 1×7²⁰. 7⁴=2401≡1 mod100? 2401−2400=1 ⇒ 7⁴≡1. So 7²⁰=(7⁴)⁵≡1 ⇒ remainder 1.

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