A composition table consists of elements which are a result of operation on the set elements.
Here we have the operation, a x10b = remainder of ab divided by 10 where a, b S.
For bS to be an inverse of aS, a x10b = e, where e is the identity element.
We know for multiplication operation we have the identity element as 1.
So e = 1.
For a = 3,
3 x10 (inverse of 3) = 1
From the table above, 3 x10 7 = 1
Hence we can conclude that ‘inverse of 3’ must be 7.
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