1. Strategy to solve complex problems Use number 1, 2, 3, 4, 5, 6, 7, 8, 9 only once so that sum of three numbers are Identical as shown below: __ + __ + __ = __ + __ + __ = __ + __ + __

2. Step 1: Determine what is known:

3. __ + __ + __ = __ + __ + __ = __ + __ + __ ? = ? = ? Step 1: Determine what is known: Sum of 1+2+3+4+5+6+7+8+9 must be the sum of a three identical numbers. 1+2+3+4+5+6+7+8+9 = 45 ? + ? + ? = 45, or ? = 15

4. Three largest digits (7,8,9) are separated. Without separating them, the sum of Two numbers would not satisfy the Condition: __ + __ + __ = 15 Or, 7+8 = 15, 7+9 = 16, 8+9 = 17.

5. Three largest digits (7,8,9) are separated. 7+8 = 15, 7+9 = 16, 8+9 = 17. 7 + __ + __ = 8 + __ + __ = 9 + __ + __ 8 7 6 6+2 5+3 6+1 5+2 4+3 4+2 5+1 More than one solution!

6. Three largest digits (7,8,9) are separated. 7+8 = 15, 7+9 = 16, 8+9 = 17. 7 + __ + __ = 8 + __ + __ = 9 + __ + __ 8 7 6 6+2 5+3 6+1 5+2 4+3 4+2 5+1 More than one solution!

7. 7 + __ + __ = 8 + __ + __ = 9 + __ + __ 8 7 6 6+2 5+3 6+1 5+2 4+3 4+2 5+1 Solution 1 Three largest digits (7,8,9) are separated. 7+8 = 15, 7+9 = 16, 8+9 = 17.

8. 7 + __ + __ = 8 + __ + __ = 9 + __ + __ 8 7 6 6+2 5+3 6+1 5+2 4+3 4+2 5+1 Solution 2 Three largest digits (7,8,9) are separated. 7+8 = 15, 7+9 = 16, 8+9 = 17.

9. Reasoning identifies every useful information. Integrates addition/subtraction & multiplication & division. Provides an opportunity to learn a strategy to solve a formidable problem. The exercise may appear to be difficult at a first glance, but becomes easy through reasoning: