Question

Consider the following discrete probability distribution. x P(x) 1 0.25 2 0.30 3 0.45 Calculate the...

  1. Consider the following discrete probability distribution.

x

P(x)

1

0.25

2

0.30

3

0.45

  1. Calculate the expected value, variance, and standard deviation of the random variable.
  2. Let y=x+5. Calculate the expected value, variance, and standard deviation of the new random variable.
  3. What is the effect of adding a constant to a random variable on the expected value, variance, and standard deviation?
  4. Let z=5x. Calculate the expected value, variance, and standard deviation of the new random variable.
  5. What is the effect of multiplying a random variable by a constant on the expected value, variance, and standard deviation?
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Answer #1

(a) We have mean as or or . The variance would be or or . The standard deviation would be or or .

(b) We have the new distribution as below.

y p(y)
6 0.25
7 0.30
8 0.45

We have mean as or or . The variance would be or or . The standard deviation would be or or .

(c) We have , and . This means that the mean increased by 5 units, the variance and standard deviation did not change. It complies with the usual rule that and .

(d) The new distribution would be as below.

z p(z)
5 0.25
10 0.30
15 0.45

We have or or . The variance would be or or . The standard deviation would be or or .

(e) We have , and . This means that the mean increased by 5 times, the variance increased by 25 (= 5 squared) times, and standard deviation increased by 5 times. It again complies with the usual rule that and .

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