Answer:
There are a total of 10 + 15 + 25 = 50 marbles in the bag, and 10 of them are red. Therefore, the probability of Tammy selecting a red marble on any given draw is 10/50 = 1/5.
Since Tammy is returning the marble to the bag after each draw, the probability of selecting a red marble on any given draw remains the same. This means that each of the 90 draws is an independent event with a probability of 1/5 of selecting a red marble.
To find the expected number of times Tammy will select a red marble in 90 draws, we can use the formula:
Expected number of red marbles = Total number of draws x Probability of selecting a red marble on any given draw
Expected number of red marbles = 90 x 1/5
Expected number of red marbles = 18
Therefore, Tammy can expect to pull out a red marble approximately 18 times in 90 draws.