All Exams Test series for 1 year @ ₹349 only
Question

What is the remainder after dividing the number 37 1000 by 9 ?

This question was previously asked in
CDS II 2021 General Knowledge Previous Year Paper (14-Nov-2021)
The correct answer is

1

Finding the Remainder using Modular Arithmetic

The question asks us to find the remainder when the large number 37 raised to the power of 1000, written as \(37^{1000}\), is divided by 9. This type of problem can be efficiently solved using the concept of modular arithmetic.

Understanding Modular Arithmetic for Remainders

Modular arithmetic deals with remainders after division. The notation \(a \equiv b \pmod{m}\) means that when \(a\) is divided by \(m\), the remainder is the same as when \(b\) is divided by \(m\). It also implies that \(a-b\) is a multiple of \(m\).

To find the remainder of a power like \(a^k\) when divided by \(m\), we can often simplify the base \(a\) first with respect to the modulus \(m\).

Step-by-Step Solution for \(37^{1000} \pmod{9}\)

Let's break down the problem:

  1. Simplify the base modulo the divisor: We first find the remainder when the base, 37, is divided by the divisor, 9.
    • Divide 37 by 9: \(37 \div 9\).
    • \(9 \times 4 = 36\).
    • The remainder is \(37 - 36 = 1\).
    • In modular notation, this is \(37 \equiv 1 \pmod{9}\). This means 37 and 1 have the same remainder when divided by 9.
  2. Apply the property of modular exponentiation: A key property in modular arithmetic states that if \(a \equiv b \pmod{m}\), then \(a^k \equiv b^k \pmod{m}\) for any positive integer \(k\).
    • Since we know \(37 \equiv 1 \pmod{9}\), we can raise both sides of the congruence to the power of 1000.
    • So, \(37^{1000} \equiv 1^{1000} \pmod{9}\).
  3. Calculate the simplified power modulo the divisor: Now we need to calculate \(1^{1000} \pmod{9}\).
    • Any positive integer power of 1 is always 1. \(1^{1000} = 1\).
    • So, \(1^{1000} \equiv 1 \pmod{9}\).
  4. State the final remainder: Combining the results from the previous steps, we have:
    • \(37^{1000} \equiv 1^{1000} \pmod{9}\)
    • \(37^{1000} \equiv 1 \pmod{9}\)
    • This means when \(37^{1000}\) is divided by 9, the remainder is 1.

Final Answer Derivation

By simplifying the base modulo 9 (\(37 \equiv 1 \pmod{9}\)), we found that calculating the remainder of \(37^{1000}\) divided by 9 is equivalent to calculating the remainder of \(1^{1000}\) divided by 9. Since \(1^{1000}\) is simply 1, the remainder is 1.

Therefore, the remainder after dividing the number \(37^{1000}\) by 9 is 1.

Modular Calculation Summary
Expression Modular Congruence Explanation
\(37 \div 9\) \(37 \equiv 1 \pmod{9}\) 37 leaves a remainder of 1 when divided by 9.
\(37^{1000} \pmod{9}\) \(37^{1000} \equiv 1^{1000} \pmod{9}\) Using the property \(a \equiv b \implies a^k \equiv b^k\).
\(1^{1000}\) \(1^{1000} = 1\) Any power of 1 is 1.
\(37^{1000} \pmod{9}\) \(37^{1000} \equiv 1 \pmod{9}\) The final remainder is 1.

Revision Table: Key Concepts in Modular Arithmetic

Modular Arithmetic Concepts
Concept Description Notation
Modulo Operation Finding the remainder after division of one number by another. \(a \pmod{m}\) (read as "a modulo m")
Congruence Modulo m Two integers \(a\) and \(b\) are congruent modulo \(m\) if they have the same remainder when divided by \(m\). Equivalently, if \(a-b\) is a multiple of \(m\). \(a \equiv b \pmod{m}\)
Properties of Congruence If \(a \equiv b \pmod{m}\) and \(c \equiv d \pmod{m}\):
  • Addition: \(a+c \equiv b+d \pmod{m}\)
  • Subtraction: \(a-c \equiv b-d \pmod{m}\)
  • Multiplication: \(ac \equiv bd \pmod{m}\)
  • Exponentiation: \(a^k \equiv b^k \pmod{m}\) for \(k \ge 0\)

Additional Information: Modular Exponentiation

Modular exponentiation is a fundamental operation in number theory and is used in various fields like cryptography. The problem \(a^b \pmod{m}\) can be computed efficiently, especially when \(b\) is very large, by repeatedly using the property \((x \times y) \pmod{m} = ((x \pmod{m}) \times (y \pmod{m})) \pmod{m}\). In our specific case, the base \(37\) simplified to \(1 \pmod{9}\), which made the calculation very simple. For more complex bases and moduli, one might use techniques like the method of repeated squaring or properties derived from Euler's Totient Theorem or Fermat's Little Theorem, although these advanced concepts were not necessary for this particular problem.

Was this answer helpful?

Similar Questions

  1. If 17 2020 is divided by 18, then what is the remainder ?

  2. What is the remainder when 27 27 - 15 27 is divided by 6?

  3. There is a remainder of 4 when a number is divided by 7.what will be the remainder. if the square of the same number is divided by 7?

  4. If the number 413283P759387 is divisible by 13, then what is the value of P?

  5. A number divides 12288, 28200 and 44333 so as to leave the same remainder in each case. What is that number?

  6. If 10 ndivides 6 23 × 75 9× 105 2, then what is the largest value of n?

  7. 710 − 510  is divisible by

  8. A is a set of positive integers such that when divided by 2, 3, 4, 5 and 6 leaves the reminder 1, 2, 3, 4 and 5 respectively. How many integers between 0 and 100 belong to the set A?

  9. 4 61 + 4 62  + 4 63  + 4 64  is divisible by

  10. Let p = 2 2n + 2 + m and q = 2 4n  - m (where n is even natural number). What should be the least value of m such that p as well as q is divisible by 5?


Important Questions from Divisibility and Remainder

  1. If the 8-digit number 888x53y4 is divisible by 72, then what is the value of (7x + 2y), for the maximum value of y?

  2. If all positive divisors of 132 are arranged in descending order, then what digit will be at unit place of first divisor ?

  3. If 3 2019 is divided by 10, then what is the remainder?

  4. The number 3798125P369 is divisible by 7. What is the value of the digit P?

  5. Consider all 3-digit numbers (without repetition of digits) obtained using three non-zero digits which are multiples of 3. Let S be their sum.

    Which of the following is/are correct?

    1. S is always divisible by 74.

    2. S is always divisible by 9.

    select the correct answer using the code given below:

Need Expert Advice?
Test Series
CDS img
Defence
UPSC CDS 2026 Mock Test Series
536 Tests 4 Tests Free
1647 Attempts
4.3(174)
English, Hindi
More Questions from CDS

Start Your Preparation with Prepp Mobile App

Download the app from Google Play & App Store
Download the app from Google Play & App Store
Prepp Mobile App