2
4
2
2
2
2
2
2
4
2
4
2
4
2(2.5)
4(1.2)
.2
2 (.4)
4 (.6)
2.5298
x
y
x
y
x
y
x
y
2
2
2
2.5
1.2
1.3
.4
.6
.7211
x
y
x
y
x
y
x
y
Example1:
Suppose that
And that X and Y are independent.
Find:
Find:
NEVER add/subtract standard deviations, always add variances first then take the square to find St. Dev.
2.5,
.4;
1.2,
.6
x
x
y
y
x
y
x
y
and
2
4
2
4
x
y
x
y
and

When does X + X + X ≠ 3X?
Answer: When doing random variable combinations!
Example2:
Suppose that on a given day the mean number of red lights you hit is 3
red lights and the standard deviation is 2 red lights.
a) What would be the mean and standard deviation of the number of

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