I've seen these types of videos before. Someone says that they can read your mind, and then gives you some math questions. You start off with a number, then do some other math, and end up with an answer that matches up to what the person in the video says it will. Usually these math tricks are very easy for me to figure out, but I ran into one that was a bit more complex. It was a video from SoFlo's facebook page that was shared by someone who is a friend of mine of facebook. The instructions went like this
Think of a number between 1 and 10
Multiply by 2
Add 5
Multiply by 50
Add 1766 if you had your birthday this year, or 1765 if you haven't
Subtract your year of birth
The first digit of the number will be the number you chose and the other two will be your age. The guy in the video says that you will get a 3 digit number. It works just fine, though if you start off with the number 10, you will get a four digit number, with the first two being the number 10. Still only a small portion of people are going to pick ten. Firstly it makes up just 10% of possible numbers for you to pick, and my guess would if you ask a large group people to think of a number between 1 and 10, less than 10% of them would think of 10.
I already knew before I did the math that it was a mathematics and not mind reading (which I don't believe in anyway), I just wanted to figure out how to break it down, and explain it, so I thought it provided a nice little challenge. In searching google I found a chat from 2004 in which someone broke down a similar problem using algebra. In their equation they used X to represent the number you started off with. I wanted to find a way to break the problem down in a less algebraic fashion. After some time of looking for patterns. I came to a conclusion. One important part of the formula is that the two numbers which you multiply in the equation are 2 and 50. If you multiply those numbers together you get 100. This assures you that the last two digits will be the same, no matter what number you start off with. If you start off with 2, then that number you end up with will be 100 greater than what you would end up with if you started with 1. You also need to make sure that the number you have before you subtract your age is one that will make the problem work. Here's a breakdown of what that number should be using some algebra, in which X represents the number you think of before doing the math, or, as I'll call it, the starting number
Current Year + 100X if your birthday has passed this year
(Current Year-1)+100X if it hasn't
The current year is 2016, lets make it more simple. The formula would then be 2016+100X, if your birthday has passed this year, or 2015+100X if it hasn't. If your starting number is 1, then the number you have before you subtract your year of birth should be 2116, or 2115 respectively. If it is 2, then it should be either 2216, or 2215. If it's 3 then you should have either 2316, or 2315. I came up with a similar formula that works
Think of a number between 1 and 10
Multiply by 4
Add 5
Multiply by 25
Add 1891 if you had your birthday this year, or 1890 if you haven't
Subtract your year of birth.
It works just the same. In fact if you take it beyond three digits numbers it works for numbers past 10. I tried the same for numbers 15, 25, 99, 100, and 1000. No matter what my starting number is, the last two digits in the answer are my the age, and the other digit(s), is the starting number. Here are some other ways to use the same math, and just changing numbers up.
Think of a number between 1 and 10
Multiply by 5
Add 5
Multiply by 20
Add 1916 if you had your birthday this year, or 1915 if you haven't
Subtract your year of birth.
Instead of adding 5 lets take the original formula, and add a different number, and come up with something that works
Think of a number between 1 and 10
Multiply by 2
Add 4
Multiply by 50
Add 1816 if you had your birthday this year, or 1815 if you haven't
Subtract your year of birth
Let's look at this problem as having different steps. Multiplying 2 is the first step, adding 4 is the second, and so on. The keys to the formula is that the numbers in step one, and three are numbers that when multiplied together give you 100, and then in step 4 you want to add a number that is going to make the problem workout.
It is also worth noting that it is no coincidence that this problem is being brought to us in a leap year. The chat about the similar equation, also came from a leap year (2004). If you were doing the problem in a year that wasn't a leap year, you may need to make a slight change for those who were born on a leap day. If the date is before March, then everything is fine. If it's after March then someone who was born on a leap day can just treat it as if their birthday has already passed in that year.
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