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A stone is dropped from the top of a building. When it crosses a point 5 m below the top, another stone starts to fall from a point 25 m below the top. Both stones reach the bottom of building simultaneously. The height of the building is:

1. 35 m
2. 45 m
3. 50 m
4. 25 m

Correct answer: 45 m

Solution

The first stone falls from the top and covers the distance of 45 m in a certain time, while the second stone, starting 25 m below the top, falls 20 m in the same time. Since both stones reach the bottom simultaneously, the total height of the building must be 45 m.

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