Remainder? No calculator allowed

What is the remainder of

1 + 2 2 + 3 3 + 4 4 + 5 5 + 6 6 + 7 7 + 8 8 + 9 9 + 1 0 10 1+2^2+3^3+4^4+5^5+6^6+7^7+8^8+9^9+10^{10}

when divided by 3 = ? 3= \ ?


The answer is 2.

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3 solutions

N 1 + 2 2 + 3 3 + 4 4 + 5 5 + 6 6 + 7 7 + 8 8 + 9 9 + 1 0 10 (mod 3) 3, 6, 9 are divisible by 3 1 + 4 + 0 + ( 3 + 1 ) 4 + ( 6 1 ) 5 + 0 + ( 6 + 1 ) 7 + ( 9 1 ) 8 + 0 + ( 9 + 1 ) 10 (mod 3) 1 + 1 + 0 + 1 4 + ( 1 ) 5 + 0 + 1 7 + ( 1 ) 8 + 0 + 1 10 (mod 3) 1 + 1 + 0 + 1 1 + 0 + 1 + 1 + 0 + 1 (mod 3) 5 2 (mod 3) \begin{aligned} N & \equiv 1+2^2+{\color{#D61F06}3^3}+4^4+5^5+{\color{#D61F06}6^6}+7^7+8^8+{\color{#D61F06}9^9}+10^{10} \text{ (mod 3)} & \small \color{#D61F06} \text{3, 6, 9 are divisible by 3} \\ & \equiv 1+4+{\color{#D61F06}0}+(3+1)^4+(6-1)^5+{\color{#D61F06}0}+(6+1)^7+(9-1)^8+{\color{#D61F06}0}+(9+1)^{10} \text{ (mod 3)} \\ & \equiv 1+1+0+1^4+(-1)^5+0+1^7+(-1)^8+0+1^{10} \text{ (mod 3)} \\ & \equiv 1+1+0+1-1+0+1+1+0+1 \text{ (mod 3)} \\ & \equiv 5 \equiv \boxed{2} \text{ (mod 3)} \end{aligned}

Thank you. I always look forward for your solutions to my problems.

Hana Wehbi - 3 years, 11 months ago

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You are welcome.

Chew-Seong Cheong - 3 years, 11 months ago
Hana Wehbi
Jun 30, 2017

1 m o d 3 = 1 1\mod 3= 1

2 2 m o d 3 = 1 2^2 \mod 3 = 1

3 3 m o d 3 = 0 3^3 \mod 3= 0

4 4 m o d 3 = 1 4^4 \mod 3 = 1

5 5 m o d 3 = 2 5^5 \mod 3 = 2

6 6 m o d 3 = 0 6^6 \mod 3=0

7 7 m o d 3 = 1 7^7 \mod 3= 1

8 8 m o d 3 = 1 8^8\mod 3= 1

9 9 m o d 3 = 0 9^9 \mod 3 =0

1 0 10 m o d 3 = 1 10^{10}\mod 3= 1

Add all the answers we get 8 m o d 3 = 2 8 \mod 3= 2 \implies the remainder is 2 \boxed{2} .

Did that to, but since you have 3 tries anyone can get the right answer because there are only 3 possible answers: 0,1,2...just saying :)

Peter van der Linden - 3 years, 11 months ago

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I usually do multiple choice but with this one l intended to make it easy to answer because no calculator allowed.

Hana Wehbi - 3 years, 11 months ago

1 1 ( m o d 3 ) 1 \equiv 1 (mod 3) 1 \Rightarrow 1

2 2 1 ( m o d 3 ) 2^2 \equiv 1 (mod 3) 1 \Rightarrow 1

3 3 0 ( m o d 3 ) 3^3 \equiv 0 (mod 3) 0 \Rightarrow 0

4 4 = 2 8 4^4 = 2^8

( 2 2 ) 4 1 4 ( m o d 3 ) (2^2)^4 \equiv 1^4 (mod 3) 1 \Rightarrow 1

5 2 1 ( m o d 3 ) 5^2 \equiv 1 (mod 3)

( 5 2 ) 2 5 1 2 5 ( m o d 3 ) (5^2)^2 \cdot 5 \equiv 1^2 \cdot 5 (mod 3)

5 ( m o d 3 ) 2 ( m o d 3 ) 5 (mod 3) \equiv 2 (mod 3) 2 \Rightarrow 2

6 6 0 ( m o d 3 ) 6^6 \equiv 0 (mod 3) 0 \Rightarrow 0

7 1 ( m o d 3 ) 7 \equiv 1 (mod 3)

7 7 1 7 ( m o d 3 ) 7^7 \equiv 1^7 (mod 3) 1 \Rightarrow 1

8 8 = 2 2 4 8^8 = 2^24

( 2 2 ) 1 2 1 1 2 ( m o d 3 ) (2^2)^12 \equiv 1^12 (mod 3) 1 \Rightarrow 1

9 9 0 ( m o d 3 ) 9^9 \equiv 0 (mod 3) 0 \Rightarrow 0

10 1 ( m o d 3 ) 10 \equiv 1 (mod 3)

1 0 10 1 10 ( m o d 3 ) 10^{10} \equiv 1^{10} (mod 3) 1 \Rightarrow 1

1 + 1 + 0 + 1 + 2 + 0 + 1 + 1 + 0 + 1 + 1 ( m o d 3 ) 1 + 1 + 0 + 1 + 2 + 0 + 1 + 1 + 0 + 1 + 1 (mod 3)

8 ( m o d 3 ) 8 (mod 3)

2 ( m o d 3 ) 2 (mod 3)

Remainder = 2 \boxed { 2 }

Thank you.

Hana Wehbi - 3 years, 11 months ago

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