Answer:
1 ×10 1 = remainder obtained by dividing 1 × 1 by 10
= 1
3 ×10 7 = remainder obtained by dividing 3 × 7 by 10
= 1
7 ×10 9 = remainder obtained by dividing 7 × 9 by 10
= 3
Composition table:
| ×10 | 1 | 3 | 7 | 9 |
| 1 | 1 | 3 | 7 | 9 |
| 3 | 3 | 9 | 1 | 7 |
| 7 | 7 | 1 | 9 | 3 |
| 9 | 9 | 7 | 3 | 1 |
The elements of first row as same as the top-most row.
1 ∈ S is the identity element with respect to ×10
3 ×10 7 = 1
Hence, the inverse of 3 is 7.