Do you have a number trick you like? I’d love if you posted it in the comments below! Also see Super Cool Math Tricks.
To begin each new school year, I like to sell Math a little. So each fall I like start the year with my favorite number trick:
1: Have a student choose an item: pen(3), book (4), board (5), or eraser (6). You can also do this with fruit of different word lengths or anything else, really. The important thing is that the words are all different lengths.
2: Have the student:
a: Turn the word into its number
b: Multiply by 5
c: Add 3
d: Double the number
e: Add in favorite single digit
3: Now ask for the number.
To “undo” the trick, simply subtract 6 (in your head is most impressive). The first digit in the number you now have corresponds to the item the student chose. The second digit is the student’s favorite number.
Let’s say we chose “eraser”. We’ll use E for “eraser”:
Let’s say my favorite number is 3:
5E + 3
Now I double it:
2(5E + 3) = 10E + 6
Add in my favorite digit “n”:
10E + 6 + n
The 10 shifts the “eraser” (E) number to the tens placement and the favorite digit is in the ones spot.
If this doesn’t work (it usually does), then I move to more drastic measures. This Prezi has embedded clips from Nova: Hunting the Hidden Dimension because it is the most awesomest Nova special (or any type of special) ever. The kids enjoyed this intro to their school year: