See the pattern? The numbers are inverted. You can also use your fingers to find out the multiplication of 9. That's what I did during my primary school days. I was so intrigued with the fact that you can use your hands to find out the multiplication of 9 and happy as I do not have to memorize the 9 timetable.
So we explored magic 9 with the problem #13 whereby we had to form a number of 2 digits from 0 - 9. After which, we had to add the 2 digits up and then put the two numbers together. Then, we have to minus the 2 digits when placed together and the sum of the 2 digits. So, what Dr Yeap did was he amazed us by getting us to tell the first digit and then he would tel us the number that we got after subtracting. At first we thought it was kind of like a magic trick which he did. But there's actually a pattern.
The number that we got after subtracting will definitely be a multiple of 9. The digit behind can be any number. It doesn't matter what number you get it will still be the same number after subtracting it.
For instance, my number is 89.
So those who know the trick will tell me that the number after subtracting is 72 (I only tell him the first digit). Basically what the person did was, he only know that the number is 80 something... He does not know the last digit. So he just add in any digit behind. He subtracted the number when placed together and the number after the 2 digits are added and he got the correct number.
If you don't believe this is the break down of all the possible numbers:
2-digit number
|
1st digit and 2nd digit add together
|
After subtracted
|
81
|
9
|
72
|
82
|
10
|
72
|
83
|
11
|
72
|
84
|
12
|
72
|
85
|
13
|
72
|
86
|
14
|
72
|
87
|
15
|
72
|
88
|
16
|
72
|
89
|
17
|
72
|
However, it is not possible to find out the 2nd number as it can be any number. And fyi, the other numbers are also multiples of 9.
2-digit number
|
1st digit and 2nd digit add together
|
After subtracted
|
12
|
3
|
9
|
27
|
9
|
18
|
34
|
7
|
27
|
46
|
10
|
36
|
52
|
7
|
45
|
69
|
15
|
54
|
74
|
11
|
63
|
89
|
17
|
72
|
92
|
11
|
81
|
Cool huh?
You can try it out on your friends and show them that you can do some Math magic!
Polygons
We also form polygons using dots template. The problem was we had to form any shape but the rule is to have one dot inside the shape. So we explored and found shapes of different sizes. We also challenged each other to find the largest shape which is 12.
Till then!
-latifahnajib
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