The mean weight of 500 college students is 70 kg and the standard deviation is 5 kg
Assuming that the weight is normally distributed, determine how many students weights:
a: Between 60 kg and 75 kg
b. More Than 90 kg
c. less than 65 kg
By condition, "a = 70\\,\\,\\sigma = 5"
a: Between 60 kg and 75 kg
Find the probability that the student's weight will be between 60 and 75 kg:
"P(60 < x < 75) = \\Phi \\left( {\\frac{{\\beta - a}}{\\sigma }} \\right) - \\Phi \\left( {\\frac{{\\alpha - a}}{\\sigma }} \\right) = \\Phi \\left( {\\frac{{75 - 70}}{5}} \\right) - \\Phi \\left( {\\frac{{60 - 70}}{5}} \\right) = \\Phi \\left( 1 \\right) + \\Phi \\left( 2 \\right) = 0,3413 + 0,4772 = {\\rm{0}}{\\rm{,8185}}"
Then quantity of students weights between 60 kg and 75 kg is
"{\\rm{500}} \\cdot {\\rm{0}}{\\rm{,8185}} \\approx {\\rm{409}}"
Answer: 409
b. More Than 90 kg
"P(x > 90) = \\Phi \\left( \\infty \\right) - \\Phi \\left( {\\frac{{90 - 70}}{5}} \\right) = \\Phi \\left( \\infty \\right) - \\Phi \\left( 4 \\right)\\approx 0,5 - 0,5 \\approx 0"
Then quantity of students weights more then 90 kg is 0.
Answer: 0
c. less than 65 kg
"P(x < 65) = P(0 < x < 65) = \\Phi \\left( {\\frac{{65 - 70}}{5}} \\right) - \\Phi \\left( {\\frac{{0 - 70}}{5}} \\right) = \\Phi \\left( {14} \\right) - \\Phi \\left( 1 \\right) = 0,5 - 0,3413= {\\rm{0}}{\\rm{,1587}}"
Then quantity of students weights less then 65 kg is "{\\rm{500}} \\cdot {\\rm{0}}{\\rm{,1587}} \\approx 79"
Answer: 79
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