In a research sample of high school students, the variable “number of instagram followers” formed normal distribution with a mean of 45 and a standard deviation of 16. if the research sample contained 500 students, approximately how many had 21 or fewer friends?
a)7
b)467
c)21
d)33

Using the normal distribution, it is found that approximately 33 students had 21 or fewer friends, given by option D.

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In a normal distribution with mean and standard deviation , the z-score 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, which is the percentile of measure X.

In this problem:

Mean of 45, thus .Standard deviation of 16, thus .The proportion with 21 or fewer followers is the p-value of Z when X = 21, thus:

has a p-value of 0.0668.

Out of 500 students:

Approximately 33 students, option D.

A similar problem is given at link

Aperecent is the answer

Step 1: 6x-10=1; step 2: 6x=11