Answer:
A) 0.10565
B) 0.33846
C)
Explanation:
The length of time that it takes for a ferry to reach a summer resort from the mainland is approximately normally distributed with a mean of 2 hours and a standard deviation of 12 minutes.
Note that, all units must be in minutes
We solve this question using z score formula
= z = (x-μ)/σ
where
x is the raw score
μ is the population mean = 2 hours
Converting to minutes
1 hour = 60 minutes
2 hour = x
Cross Multiply
x = 2 × 60 minutes
x = 120 minutes
Mean = 120 minutes
σ is the population standard deviation = 12 minutes
Over many past trips, what proportion (area) of times has the ferry reaches the island in
A) less than 1 hour, 45 minutes?
Converting 1 hour 45 minutes to minutes
60 minutes = 1 hour
Hence:
60 + 45 minutes = 105 minutes
For x < 105 minutes
= 105 - 120/12
= -1.25
Probability value from Z-Table:
P(x<105) = 0.10565
B) more than 2 hours, 5 minutes?
Converting 2 hours 5 minutes to minutes
Hence:
1 hour = 60 minutes
2 hour = x
Cross Multiply
x = 2 × 60 minutes
x = 120 minutes
Hence:
120 + 5 minutes = 125 minutes
For x < 125 minutes
z = 125 - 120/12
z = 0.41667
Probability value from Z-Table:
P(x<125) = 0.66154
P(x>125) = 1 - P(x<125) = 0.33846
C) between 1 hour, 50 minutes and 2 hours, 20 minutes?
Converting 1 hour, 50 minutes to minutes
= 60 minutes = 1 hour
Hence:
60 + 50 minutes = 110 minutes
For x = 110 minutes
= 110 - 120/12
= -0.83333
Probability value from Z-Table:
P(x = 110) = 0.20233
Converting 2 hours, 20 minutes to minutes
= 1 hour = 60 minutes
2 hour = x
Cross Multiply
x = 2 × 60 minutes
x = 120 minutes
Hence:
120 + 20 minutes = 140 minutes
For x = 140minutes
z = 140 - 120/12
= 1.66667
Probability value from Z-Table:
P(x = 140) = 0.95221