Step-by-step explanation:
There are 25 marbles altogether.
When you pick the 1st marble, there's a 5/25 chance that you pick a red marble.
When you pick the 2nd marble, there's a 15/24 chance that you pick a blue marble.
Why did it become 24? Because you already pick the 1st marble.
So since each probability is independent from each other, the total probability can be found by multiplying both probabilities, which is 1/8.
