High School

A boy threw a ball 25 times. The kinetic energy of the ball for each throw is as follows:

19.77, 20.07, 16.19, 23.11, 14.93, 20.91, 28.75, 16.23, 25.67, 19.39, 16.88, 14.46, 18.85, 20.84, 16.02, 29.22, 25.27, 17.39, 26.02, 28.42, 17.40, 20.51, 16.23, 30.05, 23.96 J.

Calculate a point estimate of the proportion of all ball throws whose energy deviation from the mean is larger than the standard deviation. Round your answer to two decimal places (e.g., 98.76).

Answer :

Rounding to two decimal places, the answer is 0.32 or 32%. First, we need to calculate the mean and standard deviation of kinetic energy for the 25 throws:

Mean = (19.77 + 20.07 + 16.19 + 23.11 + 14.93 + 20.91 + 28.75 + 16.23 + 25.67 + 19.39 + 16.88 + 14.46 + 18.85 + 20.84 + 16.02 + 29.22 + 25.27 + 17.39 + 26.02 + 28.42 + 17.40 + 20.51 + 16.23 + 30.05 + 23.96) / 25

= 21.03 J

Standard deviation = sqrt[((19.77 - 21.03)^2 + (20.07 - 21.03)^2 + ... + (23.96 - 21.03)^2) / (25 - 1)]

= 4.40 J

To find the proportion of ball throws whose energy deviation from the mean is larger than the standard deviation, we need to first determine the cutoff values that define a deviation larger than one standard deviation from the mean. The lower cutoff is the mean minus one standard deviation, and the upper cutoff is the mean plus one standard deviation:

Lower cutoff = 21.03 - 4.40 = 16.63 J

Upper cutoff = 21.03 + 4.40 = 25.43 J

Next, we count how many of the 25 throws have a kinetic energy within this range:

Number of throws with energy deviation larger than one standard deviation = 8

Therefore, the point estimate of the proportion of all ball throws whose energy deviation from the mean is larger than the standard deviation is:

Proportion = Number of throws with energy deviation larger than one standard deviation / Total number of throws

= 8 / 25

= 0.32

Rounding to two decimal places, the answer is 0.32 or 32%.

Learn more about deviation here:

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