Final answer:
The probability of picking a red or blue marble is 3/4.
Step-by-step explanation:
In this question, we are given a bag with five red marbles, four blue marbles, and three yellow marbles. When we randomly pick a marble, we want to find the probability that it is either red or blue. To do this, we need to find the total number of red and blue marbles, and divide it by the total number of marbles in the bag.
Number of red marbles: 5
Number of blue marbles: 4
Total number of marbles: 5 + 4 + 3 = 12
Probability of picking a red or blue marble = (Number of red marbles + Number of blue marbles) / Total number of marbles = (5 + 4) / 12
= 9/12
= 3/4
Therefore, the probability of picking a red or blue marble is 3/4.