The probability of selecting a blue marble at random from a jar that contains only blue, black and green marbles is 1/5 . The probability of selecting a black marble at random from the same jar is 1/4 . If the jar contains 11 green marbles, find the total number of marbles in the jar.

This answer was edited.P(blue marble) = 1/5

P(black marble) = 1/4

∴ P(green marble) = 1 – ( (1/5) + (1/4))

= 11/20

Let total number of marbles be X

then,

(11/20) × X = 11

X = 20