Holt Geometry
9-6 Geometric Probability9-6 Geometric Probability
Holt Geometry
Warm UpWarm Up
Lesson PresentationLesson Presentation
Lesson QuizLesson Quiz
Holt Geometry
9-6 Geometric Probability
Lesson Quiz: Part I
Describe the effect of each change on the area of the given figure.
The area is multiplied by 8.
1. The base length of the rectangle is multiplied by 8.
The area is multiplied by 9.
2. The radius of the circle is tripled.
Holt Geometry
9-6 Geometric Probability
Lesson Quiz: Part II
The side length is doubled.
3. A square has an area of 49 cm2. If the area is quadrupled, what happens to the side length?
4. Rob had a 10 ft by 12 ft wall painted. For a wall twice as wide, the painter charged him twice as much. Is this reasonable? Explain.
Yes; the second wall has twice the area of the first wall.
Holt Geometry
9-6 Geometric Probability
Warm UpFind the area of each figure.
1. A = 36 ft2
A = 20 m22.
3. 3 points in the figure are chosen randomly. What is the probability that they are collinear?0.2
Holt Geometry
9-6 Geometric Probability
Calculate geometric probabilities.
Use geometric probability to predict results in real-world situations.
Objectives
Holt Geometry
9-6 Geometric Probability
geometric probability
Vocabulary
Holt Geometry
9-6 Geometric Probability
Remember that in probability, the set ofall possible outcomes of an experimentis called the sample space. Any set ofoutcomes is called an event.
If every outcome in the sample space isequally likely, the theoretical probabilityof an event is
Holt Geometry
9-6 Geometric Probability
Geometric probability is used when an experiment has an infinite number of outcomes. In geometric probability, the probability of an event is based on a ratio of geometric measures such as length or area. The outcomes of anexperiment may be points on a segment or in a plane figure.
Holt Geometry
9-6 Geometric Probability
Holt Geometry
9-6 Geometric Probability
If an event has a probability p of occurring, the probability of the event not occurring is 1 – p.
Remember!
Holt Geometry
9-6 Geometric Probability
A point is chosen randomly on PS. Find the probability of each event.
Example 1A: Using Length to Find Geometric Probability
The point is on RS.
Holt Geometry
9-6 Geometric Probability
Example 1B: Using Length to Find Geometric Probability
The point is not on QR.
Subtract from 1 to find the probability that the point is not on QR.
Holt Geometry
9-6 Geometric Probability
Example 1C: Using Length to Find Geometric Probability
The point is on PQ or QR.
P(PQ or QR) = P(PQ) + P(QR)
Holt Geometry
9-6 Geometric Probability
Check It Out! Example 1
Use the figure below to find the probability that the point is on BD.
Holt Geometry
9-6 Geometric Probability
A pedestrian signal at a crosswalk has the following cycle: “WALK” for 45 seconds and “DON’T WALK” for 70 seconds.
Example 2A: Transportation Application
What is the probability the signal will show “WALK” when you arrive?
To find the probability, draw a segment to represent the number of seconds that each signal is on.
The signal is “WALK” for 45 out of every 115 seconds.
Holt Geometry
9-6 Geometric Probability
Example 2B: Transportation Application
If you arrive at the signal 40 times, predict about how many times you will have to stop and wait more than 40 seconds.
In the model, the event of stopping and waiting more than 40 seconds is represented by a segment that starts at B and ends 40 units from C. The probability of stopping and waiting more than 40
seconds is
If you arrive at the light 40 times, you will probably stop and wait more than 40 seconds about (40) ≈ 10 times.
Holt Geometry
9-6 Geometric Probability
Check It Out! Example 2
Use the information below. What is the probability that the light will not be on red when you arrive?
The probability that the light will be on red is
Holt Geometry
9-6 Geometric Probability
Use the spinner to find the probability of each event.
Example 3A: Using Angle Measures to Find Geometric Probability
the pointer landing on yellow
The angle measure in the yellow region is 140°.
Holt Geometry
9-6 Geometric Probability
Example 3B: Using Angle Measures to Find Geometric Probability
the pointer landing on blue or red
The angle measure in the blue region is 52°.
The angle measure in the red region is 60°.
Use the spinner to find the probability of each event.
Holt Geometry
9-6 Geometric Probability
Example 3C: Using Angle Measures to Find Geometric Probability
the pointer not landing on green
The angle measure in the green region is 108°.
Subtract this angle measure from 360°.
Use the spinner to find the probability of each event.
Holt Geometry
9-6 Geometric Probability
Check It Out! Example 3
Use the spinner below to find the probability of the pointer landing on red or yellow.
The probability is that the
spinner will land on red or
yellow.
Holt Geometry
9-6 Geometric Probability
Find the probability that a point chosen randomly inside the rectangle is in each shape. Round to the nearest hundredth.
Example 4: Using Area to find Geometric Probability
Holt Geometry
9-6 Geometric Probability
Example 4A: Using Area to find Geometric Probability
the circle
The area of the circle is A = r2
= (9)2 = 81 ≈ 254.5 ft2.
The area of the rectangle is A = bh
= 50(28) = 1400 ft2.
The probability is P = 254.51400
≈ 0.18.
Holt Geometry
9-6 Geometric Probability
Example 4B: Using Area to find Geometric Probability
the trapezoid
The area of the rectangle is A = bh
= 50(28) = 1400 ft2.
The area of the trapezoid is
The probability is
Holt Geometry
9-6 Geometric Probability
Example 4C: Using Area to find Geometric Probability
one of the two squares
The area of the two squares is A = 2s2
= 2(10)2 = 200 ft2.
The area of the rectangle is A = bh
= 50(28) = 1400 ft2.
The probability is
Holt Geometry
9-6 Geometric Probability
Check It Out! Example 4
Area of rectangle: 900 m2
Find the probability that a point chosen randomly inside the rectangle is not inside the triangle, circle, or trapezoid. Round to the nearest hundredth.
The probability of landing inside the triangle (and circle) and trapezoid is 0.29.Probability of not landing in these areas is 1 – 0.29 = 0.71.
Holt Geometry
9-6 Geometric Probability
Lesson Quiz: Part I
A point is chosen randomly on EH. Find the probability of each event.
1. The point is on EG.
2. The point is not on EF.
35
1315
Holt Geometry
9-6 Geometric Probability
Lesson Quiz: Part II
3. An antivirus program has the following cycle: scan: 15 min, display results: 5 min, sleep: 40 min. Find the probability that the program will be scanning when you arrive at the computer.
0.25
4. Use the spinner to find the probability of the pointer landing on a shaded area.
0.5
Holt Geometry
9-6 Geometric Probability
Lesson Quiz: Part III
5. Find the probability that a point chosen randomly inside the rectangle is in the triangle.
0.25