Brenda bakes 20 cakes a day. She does this for 9 days and then sells half of the cakes. How many cakes are left with Brenda? Let's think first. Chain of thought:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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After 9 days, Brenda bakes 20 * 9 = 180 cakes. After she sells half of them, the remaining will be 180 / 2 = 90 cakes.
Therefore, the answer is 90.