Enjoy solving math puzzles and critical thinking challenges? If so, then this challenge is just for you. The answer is also given.

## Challenge:

What is the last number in the 18th row in the following pattern?

First row: 2

Second row: 3 4

Third row: 5 6 7

Fourth row: 8 9 10 11

…

**A-** 169

**B-** 170

**C-** 171

**D-** 172

**E-** 173

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The correct answer is D.

Each row has one number more than the previous row. The first row has one number, the second row has two numbers, and the 18th row has 18 numbers.

To answer the question, we should find the number of numbers in all 18 rows.

\(1 + 2 + 3 + … + 17 + 18 = \frac{18}{2}(1+18) = 171\)

The first number starts with 2. Therefore, the last number is 172 (171 +1).