The number of cell phone minutes used by high school seniors follows a normal distribution with a mean of 500 and a standard deviation of 50. what is the probability that a student uses fewer than 400 minutes

Cumulative distribution function is written in the attached image. We know it's cumulative because the question asks sum of probabilities up to 400 minutes of cell phone usage.

where



and



GIVEN





SOLVE



plug into equation written in the attached image and calculate...



Multiply by 100 to convert to percentage.

ANSWER

There is a 2.3% chance a student uses less than 400 minutes.

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since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.