Why does 78 minus your age plus 40 work?
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How does 78 minus your age plus 40 equal the last two digits of your birth date? Transpose the instructions and add 40 to 78 first. This gives you 118, the number of years that have elapsed since this day in 1900 (today is July 25, 2018). Subtracting this from 118 gives 80, the junior two digits of your year of birth.
Regarding this, why does 79 minus your age plus 40 work?
79+40=119. That's the number of years from 1900 to 2019. Subtract your age from 119 and you'll get the year you were born. It only works well at the end of the year however, because at that point, most people will have had a birthday in the current year.
Subsequently, one may also ask, how does the birthday math trick work?
"Threes" Birthday Math Trick
- Enter the secret number.
- Multiply by 3.
- Add the secret number, then subtract 5.
- Multiply by 3, then multiply by 3 again.
- Add the secret number, then subtract the number of their favourite month (you don't have to know what month that is!)
- Multiply by 3, then multiply by 3 again, and then again a third time.
A Beddian Birthday occurs when the age a person is turning, is the same number as the last two digits of their birth year. The Beddian birthday is named for NYC firefighter Bobby Beddia who noted this coincidence. Someone born in 2015, will experience their Beddian Birthday when they are 15!