sandy wrote:
39 points are placed inside or on the surface of a perfect sphere.If 60% or less touch the surface, what is the maximum number of segments which, if connected from those points to form chords, could be diameter of the sphere?
A. 7
B. 11
C. 13
D. 23
E. 38
Here's how I solved it:
There are 39 points that are inside the sphere. Of those 39 points, 60% or less touch the surface. In other words, the percentage of points that touch the surface are between 0% and 60%, with the result being an integer.
60% of 39 is 23.4, so there has to exist a percentage slightly less than 60% that yields a total of 23 points on the surface of the sphere (it's about 58.97% of 39).
Since 23 is maximum number of points on the surface (given the parameters), to make the diameter, we would need pairs of points.
Therefore, we could make a maximum of 11 diameters, with one point without a pair, giving the answer B.