Stats Problem

• Apr 30th 2009, 06:23 AM
Mike123
Stats Problem
Hello,

Could someone please let me know what they got as the answer for this question:

A company selling vegetable seeds in packets of 40 estimates that the mean number of seeds that will actually grow is 36.0 with a standard deviation of 1.8 seeds. If a customer buys 9 different seed packets, what are the expected value and standard deviation of the number of bad seeds? Assume that packets are independent of each other.

a. μ = 108.00, σ = 16.2

b. μ = 324, σ = 5.40

c. μ = 108.00, σ = 5.40

d. μ = 324, σ = 145.8

e. μ = 324, σ = 16.2

Thank you
• May 1st 2009, 05:55 AM
mr fantastic
Quote:

Originally Posted by Mike123
Hello,

Could someone please let me know what they got as the answer for this question:

A company selling vegetable seeds in packets of 40 estimates that the mean number of seeds that will actually grow is 36.0 with a standard deviation of 1.8 seeds. If a customer buys 9 different seed packets, what are the expected value and standard deviation of the number of bad seeds? Assume that packets are independent of each other.

Mr F says: I don't agree with any of the options given below. If the question was asking for the expected value and standard deviation of the number of good seeds, then one of the options below is correct.

a. μ = 108.00, σ = 16.2

b. μ = 324, σ = 5.40

c. μ = 108.00, σ = 5.40

d. μ = 324, σ = 145.8

e. μ = 324, σ = 16.2

Thank you

Let X be the random variable number of good seeds in a packet. Then E(X) = 36.0 and var(X) = 1.8^2.

Let Y be the random variable number of good seeds in 9 packets. Then Y = 9X.

E(Y) = 9E(X) = ....

Var(Y) = 9^2 Var(X) => sd(Y) = 9 sd(X) = ....