I found this answer on the Internet. *If* it were an original answer, below is how I would grade it and why. The Chord Intersection Theorem:
If 2 chords of a circle are AB and CD and they intersect at E, then
AE * EB - CE * ED.
Problem.
Two Chords AB and CD intersect at E. If AE = 2cm, EB = 4 and CE = 2.5 cm, find the length of ED.
By the above theorem: 2*4= 2.5 * ED
ED = (2 * 4)/2.5
3.2 cm.