1. Binomial Distributions
8-6
Binomial Distributions
Warm Up
Lesson Presentation
Lesson Quiz
Holt McDougal Algebra 2
Holt Algebra 2

2. Evaluate each expression. 3. 4C3 4. (0.25)0
Warm Up
Expand each binomial.
1. (a + b) (x – 3y)2
Evaluate each expression.
3. 4C (0.25)0
% of 37
x2 – 6xy + 9y2
a2 + 2ab + b2 4 1
8.584

3. Objectives
Use the Binomial Theorem to expand a binomial raised to a power.
Find binomial probabilities and test hypotheses.

4. Vocabulary
Binomial Theorem
binomial experiment
binomial probability

5. You used Pascal’s triangle to find binomial expansions in Lesson 6-2
You used Pascal’s triangle to find binomial expansions in Lesson 6-2. The coefficients of the expansion of
(x + y)n are the numbers in Pascal’s triangle, which are actually combinations.

6. The pattern in the table can help you expand any binomial by using the Binomial Theorem.

7. Example 1A: Expanding Binomials
Use the Binomial Theorem to expand the binomial.
(a + b)5
The sum of the exponents for each term is 5.
(a + b)5 = 5C0a5b0 + 5C1a4b1 + 5C2a3b2 + 5C3a2b3 + 5C4a1b4 + 5C5a0b5
= 1a5b0 + 5a4b1 + 10a3b2 + 10a2b3 + 5a1b4 + 1a0b5
= a5 + 5a4b + 10a3b2 + 10a2b3 + 5ab4 + b5

8. Example 1B: Expanding Binomials
Use the Binomial Theorem to expand the binomial.
(2x + y)3
(2x + y)3 = 3C0(2x)3y0 + 3C1(2x)2y1 + 3C2(2x)1y2 + 3C3(2x)0y3
= 1 • 8x3 • • 4x2y + 3 • 2xy2 + 1 • 1y3
= 8x x2y + 6xy2 + y3

9. In the expansion of (x + y)n, the powers of x decrease from n to 0 and the powers of y increase from 0 to n. Also, the sum of the exponents is n for each term. (Lesson 6-2)
Remember!

10. Check It Out! Example 1a
Use the Binomial Theorem to expand the binomial.
(x – y)5
(x – y)5 = 5C0x5(–y)0 + 5C1x4(–y)1 + 5C2x3(–y)2 + 5C3x2(–y)3 + 5C4x1(–y)4 + 5C5x0(–y)5
= 1x5(–y)0 + 5x4(–y)1 + 10x3(–y)2 + 10x2(–y)3 + 5x1(–y)4 + 1x0(–y)5
= x5 – 5x4y + 10x3y2 – 10x2y3 + 5xy4 – y5

11. Check It Out! Example 1b
Use the Binomial Theorem to expand the binomial.
(a + 2b)3
(a + 2b)3 = 3C0a3(2b)0 + 3C1a2(2b)1 + 3C2a1(2b)2 + 3C3a0(2b)3
= 1 • a3 • • a2 • 2b + 3 • a • 4b2 + 1 • 1 • 8b3
= a3 + 6a2b + 12ab2 + 8b3

12. A binomial experiment consists of n independent trials whose outcomes are either successes or failures; the probability of success p is the same for each trial, and the probability of failure q is the same for each trial. Because there are only two outcomes, p + q = 1, or q = 1 - p. Below are some examples of binomial experiments:

13. Suppose the probability of being left-handed is 0
Suppose the probability of being left-handed is 0.1 and you want to find the probability that 2 out of 3 people will be left-handed. There are 3C2 ways to choose the two left-handed people: LLR, LRL, and RLL. The probability of each of these occurring is 0.1(0.1)(0.9). This leads to the following formula.

14. Example 2A: Finding Binomial Probabilities
Jean usually makes half of her free throws in basketball practice. Today, she tries 3 free throws. What is the probability that Jean will make exactly 1 of her free throws?
The probability that Jean will make each free throw is
, or 0.5.
Substitute 3 for n, 1 for r,
0.5 for p, and 0.5 for q.
P(r) = nCrprqn-r
P(1) = 3C1(0.5)1(0.5)3-1
= 3(0.5)(0.25) = 0.375
The probability that Jean will make exactly one free throw is 37.5%.

15. Example 2B: Finding Binomial Probabilities
Jean usually makes half of her free throws in basketball practice. Today, she tries 3 free throws. What is the probability that she will make at least 1 free throw?
At least 1 free throw made is the same as exactly 1, 2, or 3 free throws made.
P(1) + P(2) + P(3)
C2(0.5)2(0.5) C3(0.5)3(0.5)3-3
= 0.875
The probability that Jean will make at least one free throw is 87.5%.

16. Check It Out! Example 2a
Students are assigned randomly to 1 of 3 guidance counselors. What is the probability that Counselor Jenkins will get 2 of the next 3 students assigned?
The probability that the counselor will be assigned 1 of the 3 students is .
Substitute 3 for n, 2 for r,
for p, and for q.
The probability that Counselor Jenkins will get 2 of the next 3 students assigned is about 22%.

17. Check It Out! Example 2b
Ellen takes a multiple-choice quiz that has 5 questions, with 4 answer choices for each question. What is the probability that she will get at least 2 answers correct by guessing?
At least 2 answers correct is the same as exactly 2, 3, 4, or 5 questions correct.
The probability of answering a question correctly is 0.25.
P(2) + P(3) + P(4) + P(5)
5C2(0.25)2(0.75) C3(0.25)3(0.75) C4(0.25)4(0.75) C5(0.25)5(0.75)5-5 

18. Example 3: Problem-Solving Application
You make 4 trips to a drawbridge. There is a 1 in 5 chance that the drawbridge will be raiseD when you arrive. What is the probability that the bridge will be down for at least 3 of your trips?

19. Understand the Problem
Example 3 Continued 1
Understand the Problem
The answer will be the probability that the bridge is down at least 3 times.
List the important information:
• You make 4 trips to the drawbridge.
• The probability that the drawbridge will be down is

20. Example 3 Continued 2
Make a Plan
The direct way to solve the problem is to calculate P(3) + P(4).

21. Example 3 Continued
Solve 3
P(3) P(4)
= 4C3(0.80)3(0.20) C4(0.80)4(0.20)4-3
= 4(0.80)3(0.20) + 1(0.80)4(1) = =
The probability that the bridge will be down for at least 3 of your trips is

22. Example 3 Continued 4
Look Back
The answer is reasonable, as the expected number of trips the drawbridge will be down is of 4, = 3.2, which is greater than 3.
So the probability that the drawbridge will be down for at least 3 of your trips should be greater than

23. Check It Out! Example 3a
Wendy takes a multiple-choice quiz that has 20 questions. There are 4 answer choices for each question. What is the probability that she will get at least 2 answers correct by guessing?

24. Understand the Problem
Check It Out! Example 3a Continued 1
Understand the Problem
The answer will be the probability she will get at least 2 answers correct by guessing.
List the important information:
• Twenty questions with four choices
• The probability of guessing a correct answer is .

25. Check It Out! Example 3a Continued2
Make a Plan
The direct way to solve the problem is to calculate P(2) + P(3) + P(4) + … + P(20).
An easier way is to use the complement. "Getting 0 or 1 correct" is the complement of "getting at least 2 correct."

26. Check It Out! Example 3a Continued
Solve 3
Step 1 Find P(0 or 1 correct).
P(0) P(1)
= 20C0(0.25)0(0.75) C1(0.25)1(0.75)20-1
= 1(0.25)0(0.75) (0.25)1(0.75)19  
Step 2 Use the complement to find the probability.
1 – 
The probability that Wendy will get at least 2 answers correct is about 0.98.

27. Check It Out! Example 3a Continued4
Look Back
The answer is reasonable since it is less than but close to 1.

28. Check It Out! Example 3b
A machine has a 98% probability of producing a part within acceptable tolerance levels. The machine makes 25 parts an hour. What is the probability that there are 23 or fewer acceptable parts?

29. Understand the Problem
Check It Out! Example 3b Continued 1
Understand the Problem
The answer will be the probability of getting 1–23 acceptable parts.
List the important information:
• 98% probability of an acceptable part
• 25 parts per hour with 1–23 acceptable parts

30. Check It Out! Example 3b Continued2
Make a Plan
The direct way to solve the problem is to calculate P(1) + P(2) + P(3) + … + P(23).
An easier way is to use the complement. "Getting 23 or fewer" is the complement of "getting greater than 23.“ Find this probability, and then subtract the result from 1.

31. Check It Out! Example 3b Continued
Solve 3
Step 1 Find P(24 or 25 acceptable parts).
P(24) P(25)
= 25C24(0.98)24(0.02) C25(0.98)25(0.02)25-25
= 25(0.98)24(0.02)1 + 1(0.98)25(0.02)0  
Step 2 Use the complement to find the probability.
1 – 
The probability that there are 23 or fewer acceptable parts is about 0.09.

32. Check It Out! Example 3b Continued4
Look Back
Since there is a 98% chance that a part will be produced within acceptable tolerance levels, the probability of 0.09 that 23 or fewer acceptable parts are produced is reasonable.

33. Lesson Quiz: Part I
Use the Binomial Theorem to expand each binomial.
1. (x + 2)4
2. (2a – b)5
A binomial experiment has 4 trials, with p = 0.3.
3. What is the probability of 1 success?
4. What is the probability of at least 2 successes?
x4 + 8x3 + 24x2 + 32x + 16
32a5 – 80a4b + 80a3b2 – 40a2b3 + 10ab4 – b5
0.4116
0.3483

34. Lesson Quiz: Part II
A binomial experiment has 4 trials, with p = 0.3.
5. There is a 10% chance that Nila will have to wait for a train to pass as she heads for school. What is the probability that she will not have to wait for a train all 5 days this week?
6. Krissy has 3 arrows. The probability of her hitting the target is . What is the probability that she will get at least one arrow on the target?
about 59%
78.4%