1. Calculator Tricks 3 By Brian Carruthers (Please see notes on slide 1)

2. The answer will always be 37 Think of a four-digit number and enter it twice into your calculator. For example: 12341234

3. I think that the number you have chosen is divisible by 137

4. Don’t you believe me? Why don’t you check this on your calculator?

5. Now divide your eight-digit number by your original four-digit number

6. Guess what? The answer is 73

7. How did I know?

8. Watch This: Entering a four-digit number twice (12341234) is the same as multiplying it by 10001. (1234 x 10001 = 12341234).

9. Because 10001 = 73 x 137: the eight-digit number will be divisible by 73, 137, and your original four-digit number.

10. What did you think of that? Isn’t Maths amazing?