You're looking for a value

such that

Because the distribution is symmetric, the value of

in either case will be the same.
Now, because the distribution is continuous, you have that

The mean for the standard normal distribution is

, and because the distribution is symmetric about its mean, it follows that

.

You can consult a

score table to find the corresponding score for this probability. It turns out to be

.
Answer:
3.1 inches
Step-by-step explanation:
Area of the cookie =Pi r^2
Pi = 3.14
Diameter = 2inches
Radius r = diameter/2 = 2/2
= 1
Therefore
Area = 3.14 x 1^2
= 3.14 x 1 x 1
= 3.1 inches
He has 12 marbles.
There you go