The image contains a pattern puzzle in which the numbers inside the triangles are related to the numbers on the outside. To solve this, let's examine the first two triangles and identify the pattern to apply to the third.

1st Triangle:

• Outside numbers: 5, 5, 9
• Inside number: 20 $(5 + 5) \times 2 = 10 \times 2 = 20$

2nd Triangle:

• Outside numbers: 8, 8, 9
• Inside number: 8 $(8 + 8) \div 2 = 16 \div 2 = 8$

3rd Triangle:

• Outside numbers: 7, 11, 5
• Inside number: ?

Following the same logic, let's apply the same rule: $(7 + 11) \div 2 = 18 \div 2 = 9$

Therefore, the missing number inside the third triangle is 9.

Let me know if you need further details or explanations!

Related questions:

1. Can we find other possible patterns in the puzzle?
2. Are there other similar puzzles involving geometric shapes and numbers?
3. How can we identify different types of arithmetic sequences from patterns like these?
4. What strategies are useful in solving such puzzles quickly?
5. Can you try solving this by reversing the operations and identifying the pattern?

Tip:

When solving puzzles, always check for arithmetic operations (addition, subtraction, multiplication, division) between numbers, as these are common techniques used to create patterns.