20 out of 45 students attended the concert; 12 out of 25 students attended the concert

No; 20/45 and 12/25 are not equivalent.

Main idea on left, details on right

Skew lines(segments) are lines(segments) in 3 dimensions that do not intersect the given segment and are not parallel to it.  ae, bf, eg, and fh are your skew segments.  i hope that : )