the probability that the marble she chooses is not blue can be solve in two ways.
first way: is to solve the probability of red and yellow marbles, so that is the probability of not getting blue
P = 6 + 8 / 6 + 8 + 18P = 7/16
2nd way: is to solve the null of blue or 1 minus the probabilty of choosing blue marble
P = 1 - (18 / 6 + 8 + 18)P = 1 - ( 9 / 16)P = 7/16
