Answer:
Mean is 12.13 months
Standard deviation is 1.29
Step-by-step explanation:
We need to use z-score here
Let the mean of the distribution be a while the standard deviation be b
Mathematically;
z-score = (x-mean)/SD
We can obtain the probability from the z-score
Now, for the 10th month
The z-score for a probability of P = 0.05(5%)
Can be obtained from the standard normal distribution table and that is;
-1.645
Hence;
-1.645 = (10 - a)/b
-1.645 b = 10 - a
a = 10 + 1.645b ••••••(i)
For the 13 month, we have a proportion of 75%
The z-score corresponding to P(0.75) is = 0.674 from standard normal distribution table
Hence;
0.674 = (13-a)/b
0.674b = 13 - a
a = 13 - 0.674b. •••••(ii)
Now equate both a;
10 + 1.645b = 13 - 0.674b
13-10 = 1.645 b+ 0.674b
3 = 2.319b
b = 3/2.319
b = 1.294
So the mean a will be
10 + 1.645b = 10 + 1.645(1.294) = 10 + 2.13
So mean is 12.13
Answer:
2.00085 * 10^8
Step-by-step explanation:
