There are nine possible combinations as follows: bb, bc, bt, cb, cc, ct, tb, tc, tt, each having a probability of 1/9. The four combinations with a cab exactly one time are: bc, cb, ct, tc. Therefore the probability that she'll use a cab exactly one time is: 4/9.
Remember: 50% means 1/2. So, if 18 is 50%, or 1/2, of a number, the number must be double 18.
18 x 2 = 36
18 is 50% of 36.
The circumcenter is the point that is equidistant from each vertex
