Question

A student who is trying to write a paper for a course has a choice of two topics, A and B. If topic A is chosen, the student will order two books through interlibrary loan, whereas if topic B is chosen, the student will order four books. The student believes that a good paper necessitates receiving and using at least half the books ordered for either topic chosen. If the probability that a book ordered through interlibrary loan actually arrives in time is .9 and books arrive independently of one another, which topic should the student choose to maximize the probability of writing a good paper? What if the arrival probability is only .5 instead of .9?

Answer 1

`\text{For topic A }:0.99\\\text{For Topic B}: 0.6875`

Explanation:

Topic A: Two books are ordered

Topic B: Four books are ordered

Let X= number of books arrived

The probability that a book actually arrives in time is 0.9

i.e., p=0.9

For Topic A:

`P(X\geq 1)=P(X=1)+P(X=2)\\\Rightarrow P(X\geq 1)= \;^2C_1 (0.9)^1(0.1)^(2-1)+\;^2C_2 (0.9)^2(0.1)^(2-2)\\\Rightarrow P(X\geq 1)=0.18+0.81\\\Rightarrow P(X\geq 1)=0.99`

For Topic B:

`P(X\geq 2)=P(X=2)+P(X=3)+P(X=4)\\\Rightarrow P(X\geq 2)=1-[P(X=0)+P(X=1)]\\\Rightarrow P(X\geq 2)=1-[\;^4C_0(0.5)^0(0.5)^4 +\;^4C_0(0.5)^1(0.5)^3]\\\Rightarrow P(X\geq 2)=1-[0.0625+0.25]\\\Rightarrow P(X\geq 2)=0.6875`