Problem of the Week for Middle School

Question: 

The number of ants in Karen's ant farm doubles every day. On Sunday, there are 12,288 ants in the farm. When was the last day when there were fewer than 1,000 ants? 

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Answer: There were fewer than 1,000 ants on Wednesday.

Solution: If the number of ants doubles every day, then there were half as many each day before. So, there were 12,288 ÷ 2 = 6,144 ants on Saturday. On Friday, there were 3,072 ants. On Thursday, there were 1,536 ants. On Wednesday, there were 768 ants. Wednesday was the last day when there were fewer than 1,000 ants.