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sweet-ann [11.9K]

3 years ago

9

A school psychologist at a large high school took a random sample of 16 students and asked how much sleep they get on a typical

weekend night. The sample data were roughly symmetric with a mean of 8.75 hours and a standard deviation of 1.5 hours

1 answer:

puteri [66]3 years ago

7 0

Answer:

8.75 +/- 0.657

Step-by-step explanation:

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H=255-21t-16t^2<br><br> PLEASE HELP!!

Colt1911 [192]

Answer:

3.15 seconds is the answer.

<u>Explanation</u>

when the ball touches the ground, h =0

hence,

0=255-21t-16t²

16t²+21t-225=0

here a=16 ,b=21, c= -225

$t= \frac{ - b± \sqrt{ {b }^{2} - 4ac} }{2a} \\ \\ t= \frac{ - 21± \sqrt{ {21}^{2} - 4 \times 16 \times - 225} }{2 \times 16} \\ = \frac{ - 21 ± \sqrt{441 - ( - 14400)} }{32} \\ = \frac{ - 21± \sqrt{14841} }{32} \\ = \frac{ - 21±121.82}{32} \\ \\ t = \frac{ - 21 + 121.82}{32} \: or \: \: t = \frac{ - 21 - 121.82}{32} \\ t = 3.15 \: \: or \: \: t = - 4.46$

time cannot be negative, hence t = -4.46 can be avoided

The ball takes 3.15 seconds to hit the ground.

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