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%
