Question 47063
Say that in the 1st second, the distance covered is a.
It takes 10 seconds to reach the top.
For every second the distance doubles
sec distance
(1) a
(2) 2a
(3) 4a
(4) 8a
(5) 16a
(6) 32a
(7) 64a
(8) 128a
(9) 256a
(10) 512a
so, at the end of 8 sec the total distance covered is
a + 2a + 4a + 8a + 16a + 32a + 64a + 128a = 255a
At the end of 10 sec the top is reached and the distance covered is
a + 2a + 4a + 8a + 16a + 32a + 64a + 128a + 256a + 512a = 1023a
The fraction of the building height covered in 8 sec is
255a / 1023a = .2493