At the start, you have 10 marbles in total and 6 red marbles. The probability of the first event is 6/10.
Since you do not place the marble back in, you now have 9 marbles in total and 3 blue marbles. This probability of the second event is 3/9.
To find the probability of both events occurring, we multiply the two probabilities together. (6•3)/(10•9)=18/90=1/5
Thus, there is a 20% chance of drawing a red marble then a blue marble without placing the red marble back in the bag.