Answer:
c. 3.6 and 10.4 hrs
Step-by-step explanation:
The Empirical Rule states that, for a normally distributed random variable:
68% of the measures are within 1 standard deviation of the mean.
95% of the measures are within 2 standard deviations of the mean.
99.7% of the measures are within 3 standard deviations of the mean.
In this problem, we have that:
Mean 7, standard deviation 1.7.
For about 95% of students, nightly amount of sleep is between
7 - 2*1.7 = 7 - 3.4 = 3.6 hours
7 + 2*1.7 = 7 + 3.4 = 10.4 hours
So the correct answer is:
c. 3.6 and 10.4 hrs
Using the distribution method:
x^2 + 12x - 8x = 14 + x^2 - 4x
x^2 + 4x = x^2 - 4x + 14
Now, I'm isolating x by moving all the x's onto one side of the equation:
x^2 - x^2 + 4x + 4x = 14
Combine like terms (x^2 cancels out):
8x = 14
x = 14/8
Simplified: x = 7/4
