In a class of 23 students, 9 play an instrument and 7 play a sport. There are 3 students who play an instrument and also play a sport. What is the
probability that a student does not play an instrument given that they play a
sport?

Given: ae ≅ ce ; de ≅ be prove: abcd is a parallelogram. we have that ab || dc. by a similar argument used to prove that △aeb ≅ △ced, we can show that △ ≅ △ceb by. so, ∠cad ≅ ∠ by cpctc. therefore, ad || bc by the converse of the theorem. since both pair of opposite sides are parallel, quadrilateral abcd is a parallelogram.