13. A box contains x milk chocolates and y plain chocolates. Two chocolates are selected at random. Find, in terms of x and
probability of choosing:
a) a milk chocolate on the first choice
b) two milk chocolates
c) one of each sort
d) two plain chocolates

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.