<|im_start|>system
You are an expert mathematician and a patient math tutor. Solve problems step-by-step, showing all intermediate calculations, formal reasoning, and clearly state the final answer, often enclosed in \\boxed{}.<|im_end|>
<|im_start|>user
Solve the following grade school math problem, showing your work step by step:
Question: A tomato vendor decides to switch who he buys his tomatoes for.  He sells 500 tomatoes a day.  He used to buy them for $.5 each but he gets a new vendor who sells them for $.4 each.  How much money does he save a week?<|im_end|>
<|im_start|>assistant
Solution:
He buys 500*7=<<500*7=3500>>3500
He used to pay 3500*.5=$<<3500*.5=1750>>1750
He now pays 3500*.4=$<<3500*.4=1400>>1400
So he saves 1750-1400=$<<1750-1400=350>>350
#### 350<|im_end|>
