Answer:
The mean sleep time is 16.54 hours per day for newborn babies
Step-by-step explanation:
* Lets explain how to solve the problem
Percentiles are used to compare data across a larger sample.
To calculate the percentile, you will need to know the score, the mean
and the standard deviation.
In the problem you have the percentile and you want to find the mean.
To do that we must find z-score for the percentile from the normal
distribution table.
If the percentile lower than the 50th percentile, you will get a negative
z-score.
z-score = (x - μ)/σ, where x is the score , μ is the mean and σ is the
standard deviation
A sleep time of 15.9 hours per day for a newborn baby
x = 15.9 hours
At the 10th percentile of the distribution of sleep times for all newborn
babies
That means we want to find z-score corresponding to 0.1 (10/100 = 0.1)
By using the normal distribution table
z = -1.28
The standard deviation is 0.5 hour
σ = 0.5
Substitute these values in the rule above
-1.28 = (15.9 - μ)/0.5
Multiply both sides by 0.5
-0.64 = 15.9 - μ
Add μ to both sides
-0.64 + μ = 15.9
add -0.64 to both sides
μ = 15.9 + 0.64 = 16.54
The mean sleep time is 16.54 hours per day for newborn babies