He ate 8/2=<<8/2=4>>4 slices

So he ate 4*300=<<4*300=1200>>1200 calories

# Answer

1200
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Bob orders a pizza with 8 slices.  He eats half of it and each slice was 300 calories.  How many calories did he eat?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
1200
Bob orders a pizza with 8 slices.  He eats half of it and each slice was 300 calories.  How many calories did he eat?
train