Ask the person to which you will perform the trick to choose two different digits. Tell him/her to add them. Then tell him/her to add the last digit (of the first two digits) to the result obtained. The person should perform the same sequence of addition until he/she gets 10 numbers.

Example:

3 + 7 = 10, 7 + 10 = 17, 10 + 17 = 27, 17 + 27 = 44 …

Ask for the person to show the list of 10 numbers obtained. Now ask her/him to calculate the sum. After 5 seconds you should say the result, which for our example is 2046.

How can we know the result so fast? The trick is that the sequence of numbers obtained follows a Fibonacci sequence. To achieve the desired sum, we need only to multiply the seventh number of the sequence by 11. Thus, 186 × 11 = 2046.