The world's tallest skyscraper took seven years to build. Each year the workmen were able to double its height. How many years did it take for the skyscraper to reach half of its maximum height?
Common Wrong Answers
“Seven years”
If the skyscraper took seven years to reach its maximum height, it could not have reached half of its height at that point. It would be at its maximum height, not half.
“Five years”
After five years, the skyscraper would have doubled its height twice already, but it would not yet be at half of its maximum height, as it would still need one more year to reach that point.
“Four years”
After four years, the skyscraper would be at a quarter of its maximum height, not half. It requires three more years of doubling to reach half.
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