## 10 May 2018

### Odd or even

A person has an even number of chips in one hand and an odd number on the other. You can guess which hand the chips are in even number by doing the following:
1. Tell the person to multiply the number of the right hand by any even number and the number of left hand for any odd number;
2. Ask the person to add the two numbers obtained in 1 and to tell you the units digit;
3. If the number obtained in $2$ is odd, the even number of chips is in the right hand. If it is even, it is the left hand.