In: Statistics and Probability
1)
A normal population has a mean of 100 and a standard deviation of 10. You select a random sample of 25. What is the probability that the sample mean calculated will be between 98 and 101?
a. |
0.5328 |
|
b. |
0.3413 |
|
c. |
.0273 |
|
d. |
0.682 |
2)
A normal population has a mean of 100 and a standard deviation of 10. You select a random sample of 25. What is the probability that the sample mean calculated will be less than 98?
a. |
.25 |
|
b. |
0.1915 |
|
c. |
.1587 |
|
d. |
0.3413 |
A normal population has a mean of 100 and a standard deviation of 10. You select a random sample of 25. What is the probability that the sample mean will be greater than 101?
a. |
0.3085 |
|
b. |
0.1915 |
|
c. |
.25 |
|
d. |
0.5 |
Solution :
= / n = 10 / 25 = 2
1)
= P[(98 - 100) / 2< ( - ) / < (101 - 100) / 2)]
= P(-1 < Z < 0.5)
= P(Z < 0.5) - P(Z < -1)
= 0.6915 - 0.1587
= 0.5328
Probability = 0.5328
option a. is correct
2)
P( < 98) = P(( - ) / < (98 - 100) / 2)
P(z < -1)
= 0.1587
Probability = 0.1587
option c. is correct
3)
P( > 101) = 1 - P( < 101)
= 1 - P[( - ) / < (101 - 100) / 2]
= 1 - P(z < 0.5)
= 1 - 0.6915
= 0.3085
Probability = 0.3085
option a. is correct