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Difficulty: 3/102024 NMTC 2024 (QII-34)

What is the units digit of * ?

Guide / Hint

Hint 1: Find the units digit of using the cyclicity of 2 (period 4). The remainder of 2047 mod 4 is 3, giving 8.

Hint 2: Find the units digit of using the cyclicity of 3 (period 4). The remainder of 11 mod 4 is 3, giving 7.

Hint 3: Multiply the two units digits: .

Solution

Step 1 (Units digit of 2^2047): The units digit of powers of 2 cycle with period 4: .

Step 2 (Units digit of 3^11): The units digit of powers of 3 cycle with period 4: .

Step 3 (Product Units Digit): Multiply the two units digits:

Step 4 (Conclusion): The units digit of the product is exactly 6.

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    2024 NMTC 2024 QII-34 - Olympiad Math Olympiad Question | Leminno