Question: Look at the sequence below and find the missing number:
$$\text{Triangle with } 3, 4, 5 \rightarrow 12$$$$\text{Square with } 4, 5, 6, 7 \rightarrow 22$$$$\text{Pentagon (5 sides) with } 2, 3, 4, 5, 6 \rightarrow ?$$What is the missing number?
Answer & Explanation (Lời giải):
The missing number is 20.
Explanation: The rule for each shape is to calculate the sum of all the numbers around its vertices (corners).
- For the triangle: $3 + 4 + 5 = 12$
- For the square: $4 + 5 + 6 + 7 = 22$
- For the pentagon: $2 + 3 + 4 + 5 + 6 = 20$
Therefore, the correct answer to find is 20.