UPSC Prelims 2025·CSAT·Quantitative Aptitude·Number System

If n is a natural number, then what is the number of distinct remainders of (1ⁿ + 2ⁿ) when divided by 4?

Dalvoy logo
Reviewed by Dalvoy
UPSC Civil Services preparation
Last updated 23 May 2026, 3:31 pm IST
  1. A0
  2. B1
  3. C2Correct
  4. D3

Explanation

To find the number of distinct remainders of (1^n + 2^n) when divided by 4, we analyze the expression for different values of n, where n is a natural number (n = 1, 2, 3, ...). 1. Analyze 1^n: For any natural number n, 1^n is always 1. 2. Analyze 2^n: * If n = 1: 2^1 = 2. * If n = 2: 2^2 = 4. When 4 is divided by 4, the remainder is 0. * If n = 3: 2^3 = 8. When 8 is divided by 4, the remainder is 0. * For any n >= 2, 2^n will be a multiple of 4 (since 2^n = 2^2 * 2^(n-2) = 4 * 2^(n-2)). Therefore, for n >= 2, 2^n leaves a remainder of 0 when divided by 4. Now, let's combine these for (1^n + 2^n) mod 4: * Case 1: n = 1 (1^1 + 2^1) = 1 + 2 = 3. When 3 is divided by 4, the remainder is 3. * Case 2: n >= 2 (1^n + 2^n) = 1 + (a multiple of 4) When (1 + 2^n) is divided by 4, the remainder is (1 + 0) = 1. So, the possible distinct remainders are 3 (when n=1) and 1 (when n>=2). There are 2 distinct remainders. The final answer is C.
Quantitative Aptitude: If n is a natural number, then what is the number of distinct remainders of (1ⁿ + 2ⁿ) when divided by 4?

Related questions

More UPSC Prelims practice from the same subject and topic.