Question

Use the normalcdf function on a calculator to find the probability that the battery life is 20 hours or longer for each phone.

Answer 1

Answer:

• C: 15.9%
• T: 50%

Step-by-step explanation:

The calculator results are shown in the attachment.

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For this question, the Empirical Rule is sufficient to tell you the answer to the nearest percent.

20 hours is 1 standard deviation above the mean (18+2=20) for the C phone. The empirical rule tells you that the probability of being above that value is (1 -68%)/2 = 16%, where 68% is the probability of being within 1 standard deviation of the mean.

20 hours is the mean for the T phone. You know that the normal distribution is symmetrical about its mean, so the probability of being above the mean is 50%.