Question

Please tell me a birthday trick and the solution means how to do that?

Answer 1

You, the future math whiz, start by giving your friend a calculator. Then, you issue the following sequence of instructions. Make sure your friend presses the equals button (=) after each step!

• Enter the number 7
• Multiply by the month of your birth
• Subtract 1
• Multiply by 13
• Add the day of your birth
• Add 3
• Multiply by 11
• Subtract the month of your birth
• Subtract the day of your birth
• Divide by 10
• Add 11
• Divide by 100

And, amazingly, your friend's birthday will appear on the calculator screen! For example, let's suppose your friend was born on February 29. Below, I repeat the sequence of instructions, showing the result at each step in red.

• Enter the number 7 (7)
• Multiply by the month of your birth (7x2=14)
• Subtract 1 (14-1=13)
• Multiply by 13 (13x13=169)
• Add the day of your birth (169+29=198)
• Add 3 (198+3=201)
• Multiply by 11 (201x11=2211)
• Subtract the month of your birth (2211-2=2209)
• Subtract the day of your birth (2209-29=2180)
• Divide by 10 (2180/10=218)
• Add 11 (218+11=229)
• Divide by 100 (229/100 = 2.29)