In this video clip we solve a number
bond question.
We have one two three four and five.
We want to fill them in five circles such that the three numbers
in each line have the same sum.
Okay, we first want to determine which
number to put in the center.
Suppose we want to put one there.
Then we observe the remaining four numbers. We can see 2 plus 5
equals 3 plus 4 equals 7. So that can be a solution.
So we put 1 here.  We can put 2 5
3 4, right? This is a solution.
There can be some other solutions.  We want to find all the solutions.
So be careful and patient.
Now we see whether we can put 2 in the center. If we do that,
then we have 1 3 4 5 remain. Here we can see,
if we add 1 with 5 and 3 with 4, we have 6 and 7 respectively.
They are not equal.  So two cannot be in the center.
How about 3,  3 here, okay. if we put three in the center, then we can see one
plus five equals two plus four. so that is
another solution.
Okay, now we think of 4.
Here, if we put a four in the center, then we can have one plus five
versus two plus three. They are six and five respectively, unequal.
so that doesn't work. Then how about five? We put a five in the center, we have
1 plus 4 equals 2 plus, 5, 2 plus 3, which is 5,
right? So that is a solution.
Actually that is our last solution.
You can see the order of two numbers on the boundaries of a line doesn't
matter. We can put two or
three here the other one here.
So that's all the solution. 
Assignment: we can try to fill the across
using the same logic for 2 3 4
5 6.
Try to find all the solutions.
