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The scores on a national achievement exam are normally distributed with a mean of 500
and a standard deviation of 100. If a student who took the exam is randomly selected,
find the probability that the student scored below 600. Assume a normal distribution.
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Notice that 600 is one standard deviation from the mean 500.
According to the empirical rule, 68% of all scores are within one standard deviation
from the mean.
Due to the symmetry of normal curve, it means that half of that, or 34% of all scores
are in the interval [500,600].
Add to it 50% of scores that are under the mean, and you will get the ANSWER
to the problem's question of 50% + 34% = 84%.
Solved.