A child is making a 5-level pyramid by stacking some blocks. In the first row, he has 9 blocks. For the next rows, he has 2 less than the blocks he has from its bottom row. How many blocks did he use in all?
Let's be accurate as possible. Think before you answer.
25
On the second row, he used 9 - 2 = 7 blocks.

On the third row, he used 7 - 2 = 5 blocks.

On the fourth row, he used 5 - 2 = 3 blocks.

On the fifth row, he used 3 - 2 = 1 block.

Therefore, he used a total of 9 + 7 + 5 + 3 + 1 = 25 blocks.

.

So, the final answer is 25