The answer is:

Which can be written as: [-8, infinity)
This is the interval from -8 to infinity. So -8 is our left most point on the number line and infinity being our right most. There is no boundary on the right side.
Note how the left side has a square bracket and the right side has a curved parenthesis. This isn't a typo. The square bracket tells the reader "include the endpoint -8 as part of the solution set". The parenthesis tells the reader "do NOT include the endpoint infinity as part of the solution set".
Rule: infinity and negative infinity is always paired with a parenthesis because these aren't numbers. It's impossible to reach infinity, therefore it's impossible to include it in the set of values. If you could include it, then that implies you ran out of numbers.
Answer:
68.26% probability that a randomly selected full-term pregnancy baby's birth weight is between 6.4 and 8.6 pounds
Step-by-step explanation:
Problems of normally distributed samples are solved using the z-score formula.
In a set with mean
and standard deviation
, the zscore of a measure X is given by:

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
In this problem, we have that:

What is the probability that a randomly selected full-term pregnancy baby's birth weight is between 6.4 and 8.6 pounds
This is the pvalue of Z when X = 8.6 subtracted by the pvalue of Z when X = 6.4. So
X = 8.6



has a pvalue of 0.8413
X = 6.4



has a pvalue of 0.1587
0.8413 - 0.1587 = 0.6826
68.26% probability that a randomly selected full-term pregnancy baby's birth weight is between 6.4 and 8.6 pounds