Hello, graffitihead!

We have 20 marbles in a bag, some red, some blue.

We randomly drawl a marble.

If it is blue, we receive $10. Otherwise we pay $3.

How many blue marbles are in the bag if we have an expected value of -$1.05?

Let = number of blue marbles in the bag.

Then = number of red marbles in the bag.

We have: .

The expected value is -$1.05

. .

And solve for . . .