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## Homework Statement

Calculate 7*11 + 9*11^-1 in the group Z20

## Homework Equations

## The Attempt at a Solution

77+ (9*1/11) in group Z20

77 + 9/11

17 +11x= 20mod+9

My solution was 12, this makes 149 on both sides when you multiply the mod times 7.

I am doing independent study and the computer program I am using says the answer is 16.

What am I doing wrong? Btw, what is the difference between ring congruence arithmetic and regular congruence arithmetic? They seem pretty similar.