The average height of 30 boys out of a class of 50, is 160 cm. If the average height of the remaining boys is 165 cm, the average height of the whole class (in cm) is:
A jar has 5 marbles, 1 of each of the colours red, white, blue, green, and yellow. If 4 marbles are removed form the jar, what is the probability that the yellow one was removed ?