Answer: 22 days .
Step-by-step explanation:
The simplest approach in this problem is using the z scores. That’s is computed by the fomular :z = (x - mean)/standard deviation.....(1).
In order to answer to the question .We need to find z-scores that have an area of 39% in the normal distribution plot .That means that there will be 61% on the outside of this range, and 39% within, centered around the mean.
Since we are interested in the two areas . We have 61%/2 = 30.5% .Now we have to find the z-score corresponding to a p-value of 0.305
From the normal table p-value of 0.305 corresponds with z = 0,6368 . Now we need to Plug in the value we have for z, 21 for the mean and 1 for the standard deviation in equation (1) and solve for x.
We have 0,6368 = (x-21)/1
Solving for x = 21+ 0,6368 = 21,6368 which approximately 22 .
Answer: the 10th percentile for incubation time is 21 days
