Geometry Warm ups #8
10-8 GEOMETRIC
PROBABILITY
RULE:
To find the Geometric Prob:
Area of what they ask for
Area of WHOLE shape
Example
If you threw a dart and it landed on the picture, what is the
probability that the dart lands inside the small circle?
(known as the “bull’s eye”)
Area you are trying for
Total Area
2
4
1


2
10  100
25
2
Example
A target has circles with radii of 1, 2, and 4. What is the
probability that a dart
thrown at random will
hit within:
• a) the bull’s eye?
• b) the outer ring?
• a)
b)
2
2
1
1
1

16 16
4   2  16  4

2
4
16
12 3
 
16 4
Example cont.
A target has circles with radii of 1, 2, and 4. What is the
probability that a dart
thrown at random will
hit within:
• c) the middle ring?
1
•
2   1  4  1

2
4
16
2
2
3

16
Rule
• Use for number line problems, not shapes:
• Length of Part .
Length of Whole
Example
Point K on ST is chosen at random.
What is the probability that K lies on QR?
Example
• A subway stops every 20 minutes, waits 3 minutes and
then leaves.
If you arrive at a random time, what is the prob. you will be
able to board the train?
Shortcut: It’s always “little”/”big” –Reduce when necessary!!
3_
20
TOO 
Homework
• Pg. 671-672 # 8 – 25, 40, 43