Answer: Without replacing
Step-by-step explanation:
If you don't replace the first red marble, it decreases the number of red marbles in the mix, making the proportion of blue marbles relatively larger. For example, if there were 5 red and 5 blue marbles, there would be a 50% chance of drawing a blue marble. If the red drawn is not replaced, there is a 5/9 chance of drawing a blue marble, or a 55% chance of drawing one.

Step-by-step explanation:

Answer:
k = 10.5
Step-by-step explanation:
8/7 = 12/k
Using cross products
8k = 7*12
8k = 84
Divide each side by 8
8k/8 = 84/8
k = 10.5