1st step is to find the radius, then substitute into the formula for area of a circle

to find the radius, just halve the diameter
Answer: 1/4 chance of picking red
Step-by-step explanation: There are 120 buttons in all, so the fraction of red marbles is 30/120. 30/120 = 1/4
Hope this helps!
All you have to do is move the denominator on the other side, by multiplying.
a-10
------- = -9
20
multiply 20 x -9
= -180
then it becomes a-10=-180
+10 +10
a=-170
Answer:
495
Step-by-step explanation:
This problem can be solved b using a combination. We're using a combination for this because the order in which you would pick the books doesn't matter. To solve, we would plug in the number of books, in this case 12, into the n value of the combination. Then we would plug in the number of books that would be picked, in this case 4, into the r value of the combination. Solve the combination, and you get 495.