Five twos
The nine times table
Neighborhood
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Five twos
 
How would you write all the numbers between zero and ten by using two fives, additions, subtractions, multiplications and divisions?

Example
 
0 = 2 - 2/2 - 2/2

Solutions
 
 
1
2
3
4
5

6
7
8
9
10
Neighborhood
 
We have to put numbres 1-10 in a square. Clues:
 
1's neighbors add up to 15
 
2's neighbors add up to 6
 
4's neighbors add up to 23
 
5's neighbors add up to 16
 

 
A, B, C y D are x's neighbors
 
Solution
 The nine times table

An alternative way to multiply by nine:
 
1. Number your fingers, 1-10.
 
2. Open your palms and number fingers from left to right.
 
3. For example, if you want to multiply 9x3, you have to hide finger nº3.
 
4. All the fingers from left to nº3 indicate tens. All the fingers from nº3 to right indicate units.
 
5. In this case (9x3) we have 2 fingers on the left and 7 fingers on the right (27).
 
6. This trick is easy until 9x10. Then, it becomes a little more difficult.

Demo Video