An event has probability 1 if you're certain that it will happen. You are sure to pick a marble that's either yellow, green, red, or blue. So, this probability is 1.
There are more yellow marbles than blue marbles, so it's actually more likely that you'll pick a yellow one, rather than the blue one.
The probability of picking a green marble is given by the number of green marbles divided by the total number of marbles. Compute this ratio and see what you get.
Similarly, the probability of picking a black marble is given by the number of black marbles divided by the total number of marbles. There are no black marbles, so...
Because the boarder goes around all edges, 6 in must be subtracted from 6ft and 4ft. 6ft - 6in = 5.5 ft 4ft - 6in = 3.5 ft Area of the bulletin board: (5.5)(3.5) = 19.25 ft
