It cost Benjamin $1.35 to send 9 text messages how much would it cost to send 118 text messages
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Answer:
The standard deviation of the sum is of 8.06.
Step-by-step explanation:
When the distribution is normal, we use 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.
Sum of normal variables:
When we add two normal variables, the mean is the sum of their means, and the standard deviation is the square root of the sum of their variances. In this question:
First intersection -> Standard deviation of 4
Second intersection -> Standard deviation of 7
Sum:
The standard deviation of the sum is of 8.06.