Answer:
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%.