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3 years ago

If you choose one student at random, what is the probability (±0.0001) that the student's score is between 20 and 30?

1 answer:

5 0

Z-score for 30 = (30 - 25) / 5.8 = 0.8621
z-score for 20 = (20 - 25) / 5.8 = -0.8621
:
Note find probabilities from z-tables
:
Probability ( 20 < X < 30 ) = 0.8051 - 0.1949 = 0.6102

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Suppose we roll a fair die and let X represent the number on the die. (a) Find the moment generating function of X. (b) Use the

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$M^{\prime}(0)=E(X)=\frac{1}{6}(1+2+3+4+5+6)$

$\Rightarrow E(X)=\frac{21}{6}$

$M^{\prime \prime}(t)=\frac{1}{6}\left(e^{t}+4 e^{2 t}+9 e^{3 t}+16 e^{4 t}+25 e^{5 t}+36 e^{6 t}\right)$

$M^{\prime \prime}(0)=E(X)=\frac{1}{6}(1+4+9+16+25+36)$

$\Rightarrow E\left(X^{2}\right)=\frac{91}{6}$

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