Question

6) The amount of Jen's monthly phone bill is normally distributed with a mean of $70 and a standard
deviation of $10. What percentage of her phone bills are between $40 and $100?
A) 68.26%
B) 99.99%
C) 95.44%
D) 99 74%
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7) At one college, GPA's are normally distributed with a mean of 26 and a standard deviation of 0.5.
What percentage of students at the college have a GPA between 2.1 and 3.17
A) 84.13%
B) 68.26%
C) 95.44%
D) 99.74%​

Answer 1

Answer:

i)The correct option is  D.) 99.74%

ii) The correct option is B.) 68.26%

Step-by-step explanation:

i) P(10≤X≤70) = P(  (10−40)/10  ≤Z≤   (70−40 )/10 ) =  Pr(−3≤Z≤3)

= 0.9987 - 0.0013 = 0.99734

Therefore the percentage of Jen's monthly phone bills are between $40 and $100 is D.) 99.74%

ii)P(2.1≤X≤3.1) = P(  (2.1 − 2.6) /0.5   ≤ Z  ≤ (3.1−2.6 )/0.5)  =  Pr(−1  ≤Z  ≤1) )

=  0.8413 − 0.1587  =  0.6826

Therefore the percentage of students at college have a GPA between 2.1 a,d 3.1 is B.) 68.26%