Concept explainers
a.
To explain: why the following given pattern gives the probability that the n people have distinct birthdays.
a.

Answer to Problem 70E
The probability of no two people from the group of n people sharing the same birthday is
P(E)=n(E)n(S)=365·364·363.....[365−(n−1)]365n.
Explanation of Solution
Given information: Consider a group of n people, the given pattern is,
n=2;365365·364365=365·3643652n=3;365365·364365·363365=365·364·3633653
Calculation:
The pattern gives the probability that n people have distinct birthdays using the standard formula of P(E)=n(E)n(S) . The
P(E)=n(E)n(S)=365·364·363.....[365−(n−1)]365n.
b.
To write: an expression for the probability that four people ( n =4) have distinct birthdays using the pattern in part (a).
b.

Answer to Problem 70E
n=4 ; 365365·364365·363365·362365=365·364·363·3623654
Explanation of Solution
Given information: Consider a group of n people, the given pattern is,
n=2;365365·364365=365·3643652n=3;365365·364365·363365=365·364·3633653
Calculation:
To find the probability that amongst 4 people , no 2 share the same birthday, plug n= 4 into the given pattern.
n=4 ; 365365·364365·363365·362365=365·364·363·3623654
c.
To verify: that Pn probability that the n people have distinct birthdays can be obtained recursively by
P1=1 and Pn=365−(n−1)365Pn−1.
c.

Answer to Problem 70E
Pn Probability that the n people have distinct birthdays can be obtained recursively by
P1=1 and Pn=365−(n−1)365Pn−1.
Explanation of Solution
Given information: Given Pn probability that the n people have distinct birthdays can be obtained recursively by
P1=1 and Pn=365−(n−1)365Pn−1.
Calculation:
Here, use the probability of 4 people having different birthdays as an example of how the recursive method provided is a valid way to find this probability. Using the recursive definition,
P4=365−(4−1)356P4−1=362356P3=362356·365−(3−1)356P3−1=363·3623562P2=363·3623562·365−(2−1)356P2−1=364·363·3623563P1=364·363·3623563·365365=365·364·363·3623564.
Same result using this recursive definition as the one obtained in part (b).
Hence, Verified.
d.
To explain: why Qn=1−Pn gives the probability that at least two people in a group of n people have the same birthday.
d.

Answer to Problem 70E
Qn=1−Pn .
Explanation of Solution
Given information: Qn=1−Pn gives the probability that at least two people in a group of n people have the same birthday.
Calculation:
Pn gives the probability that in a group of n people , none share the same birthday. The complement of the event is Qn , is the event that at least two people share the same birthday. Therefore, by the law of complementation, Qn=1−Pn .
e.
To complete: the given table using the result of parts (c) and (d).
e.

Answer to Problem 70E
n | 10 | 15 | 20 | 23 | 30 | 40 | 50 |
Pn | 0.88 | 0.75 | 0.59 | 0.49 | 0.29 | 0.11 | 0.03 |
Qn | 0.12 | 0.25 | 0.41 | 0.51 | 0.71 | 0.89 | 0.97 |
Explanation of Solution
Given information: Given table is,
n | 10 | 15 | 20 | 23 | 30 | 40 | 50 |
Pn | |||||||
Qn |
Calculation:
When constructing the probability of this table, it can help to recognize that:
Pn=365·364·.....[365−(n−1)]365n=365!365n(365−n)!=365Pn365n.Qn=1−Pn
The completed table shown below,
n | 10 | 15 | 20 | 23 | 30 | 40 | 50 |
Pn | 0.88 | 0.75 | 0.59 | 0.49 | 0.29 | 0.11 | 0.03 |
Qn | 0.12 | 0.25 | 0.41 | 0.51 | 0.71 | 0.89 | 0.97 |
f.
To find: how many people must be in a group so that the probability of at least two of them having the same birthday is greater than 12 , explain.
f.

Answer to Problem 70E
23 people in a group so that the probability of at least two of them having the same birthday is greater than 12 , explain.
Explanation of Solution
Given information:
n | 10 | 15 | 20 | 23 | 30 | 40 | 50 |
Pn | 0.88 | 0.75 | 0.59 | 0.49 | 0.29 | 0.11 | 0.03 |
Qn | 0.12 | 0.25 | 0.41 | 0.51 | 0.71 | 0.89 | 0.97 |
Calculation:
It is clear from the above table, 23 people must be in a group for the probability of at least two them having the same birthday to be greater than 12.
Chapter 8 Solutions
PRECALCULUS W/LIMITS:GRAPH.APPROACH(HS)
- 2. Consider the following: Prove that x, x2, and 1/x are the solutions to the homogeneous equation corresponding to x³y"" + x²y" + 2xy' + 2y = 2x4. b. use variation of parameters to find a particular solution and complete the general solution to the differential equation. I am interested in process. You may use a computer for integration, finding determinants and doing Kramer's.arrow_forward3. A spring is stretched 6 in. by a mass that weighs 8 lb. The mass is attached to a dashpot mechanism that has a damping constant of 0.25 lb-sec./ft. and is acted on by an external force of 4 cos 2t lb. a. Set-up the differential equation and initial value problem for the system. b. Write the function in phase-amplitude form. C. Determine the transient solution to the system. Show your work. d. Determine the steady state of this system. Show your work. e. Is the system underdamped, overdamped or critically damped? Explain what this means for the system.arrow_forward4. Suppose that you have a circuit with a resistance of 20, inductance of 14 H and a capacitance of 11 F. An EMF with equation of E(t) = 6 cos 4t supplies a continuous charge 60 to the circuit. Suppose that the q(0)= 8 V and the q'(0)=7. Use this information to answer the following questions a. Find the function that models the charge of this circuit. b. Is the circuit underdamped, overdamped or critically damped?arrow_forward
- 1. Solve the initial value problem: y" -11y' + 30y = x³e6x y(0) 11, y'(0) = 36 =arrow_forwardWhat is the particular solution to the differential equation y′′ + y = 1/cos t ?arrow_forwardWhich of the following is the general solution to y′′ + 4y = e^2t + 12 sin(2t) ?A. y(t) = c1 cos(2t) + c2 sin(2t) + 1/8 e^2t − 3t cos(2t)B. y(t) = c1e^2t + c2e^−2t + 1/4 te^2t − 3t cos(2t)C. y(t) = c1 + c2e^−4t + 1/12 te^2t − 3t cos(2t)D. y(t) = c1 cos(2t) + c2 sin(2t) + 1/8 e^2t + 3 sin(2t)E. None of the above. Please include all steps! Thank you!arrow_forward
- Show that i cote +1 = cosec 20 tan 20+1 = sec² O २ cos² + sin 20 = 1 using pythagon's theoremarrow_forwardFind the general solution to the differential equationarrow_forwardcharity savings Budget for May travel food Peter earned $700 during May. The graph shows how the money was used. What fraction was clothes? O Search Submit clothes leisurearrow_forward
- Exercise 11.3 A slope field is given for the equation y' = 4y+4. (a) Sketch the particular solution that corresponds to y(0) = −2 (b) Find the constant solution (c) For what initial conditions y(0) is the solution increasing? (d) For what initial conditions y(0) is the solution decreasing? (e) Verify these results using only the differential equation y' = 4y+4.arrow_forwardAphids are discovered in a pear orchard. The Department of Agriculture has determined that the population of aphids t hours after the orchard has been sprayed is approximated by N(t)=1800−3tln(0.17t)+t where 0<t≤1000. Step 1 of 2: Find N(63). Round to the nearest whole number.arrow_forward3. [-/3 Points] DETAILS MY NOTES SCALCET8 7.4.032. ASK YOUR TEACHER PRACTICE ANOTHER Evaluate the integral. X + 4x + 13 Need Help? Read It SUBMIT ANSWER dxarrow_forward
- Calculus: Early TranscendentalsCalculusISBN:9781285741550Author:James StewartPublisher:Cengage LearningThomas' Calculus (14th Edition)CalculusISBN:9780134438986Author:Joel R. Hass, Christopher E. Heil, Maurice D. WeirPublisher:PEARSONCalculus: Early Transcendentals (3rd Edition)CalculusISBN:9780134763644Author:William L. Briggs, Lyle Cochran, Bernard Gillett, Eric SchulzPublisher:PEARSON
- Calculus: Early TranscendentalsCalculusISBN:9781319050740Author:Jon Rogawski, Colin Adams, Robert FranzosaPublisher:W. H. FreemanCalculus: Early Transcendental FunctionsCalculusISBN:9781337552516Author:Ron Larson, Bruce H. EdwardsPublisher:Cengage Learning





