On the second row, he used 9 - 2 = <<9-2=7>>7 blocks.

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

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

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

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

# Answer

25
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
25
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?
train