From the context, I can guess that FJ and GI are the segments on the number line.

but I can not guess how they are placed one relative to the other.



        The final answer depends on their locations.



        The final answer may be separated and expressed in 3 parts.



1)  If the segmenths are disgoint, then the probability is zero.



2)  If the segment GI lies entirely inside of FJ  (is the subset, or a part of FJ).
    then the probability is the ratio of the length of the smaller segment GI
    to the length of the longer segment FJ.



3)  If the segments FJ and GI have partial intersection (but GI is not a part of FJ).
    then the probability is the ratio of the length of the intersection part to the
    length of the segment FJ.