I found a set of “math magic tricks” that involve different computation steps that take you to a designated end number from any starting number. When I first looked at the you’ll always get 15 as an answer equation I thought there was no way that would ever work, until I tested it, setting up an excel formula following the directions my formula [ =((((A3*3+45)*2)/6)-A3] is less than pretty but it worked and revealed how the trick works, you start with a number then remove it at the end. I tried this with several positive and negative whole and decimal numbers including Pi, it’s my favourite number. This is something I could do with my class and would amaze them but I think it might be better suited for a higher grade level than grade 4 where the students are ready to look at order of operations and how order of operations could alter the end result.
- Step 1: Think of a number, such as 279.
- Step 2: Multiply it by 3. So, 279 x 3 = 837.
- Step 3: Now add 45 to the answer. So, 837 + 45 = 882.
- Step 4: Multiply the answer by 2. So, 882 x 2 = 1764.
- Step 5: Divide this answer by 6. This will give you 1764 / 6 = 294.
- Step 6: Subtract your original number from this answer.
- Step 7: That makes it 294 – 279 = 15. Surprising, right?