# Understanding Cryptography by Christof Paar and Jan Pelzl - Chapter 1 Solutions - Ex1.6

- 1 min- Return to index
- Exercise 1.1
- Exercise 1.2
- Exercise 1.3
- Exercise 1.4
- Exercise 1.5
- Exercise 1.6
- Exercise 1.7
- Exercise 1.8
- Exercise 1.9
- Exercise 1.10
- Exercise 1.11
- Exercise 1.12
- Exercise 1.13
- Exercise 1.14

## Exercise 1.6

Compute without a calculator:

- 1/5 mod 13
- 1/5 mod 7
- 3 · 2/5 mod 7

### Solution

*I haven’t yet verified this solution independently. If you spot any mistakes, please leave a comment in the Disqus box at the bottom of the page.*

In order to perform a division by , we must find the multiplicative inverse and multiply by it.

1.

2.

3.