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When $N$ is divided by $10$, the remainder is $a$. When $N$ is divided by $2$, the remainder is $b$. What is $N$ modulo $20$, in terms of $a$ and $b$?

 Aug 14, 2024
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N mod 10 = a

N mod 2 = b

N mod 20 =?

2 and 10 are not coprime. 10 is multiple of 2.

If a is odd then b=1.

If a is even then b=0.

We don’t need b.

N mod 20 ={a, a+10}

 Aug 14, 2024

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