In: Statistics and Probability
Q3.(15) The SAT scores for US high school students are normally distributed with a mean of 1500 and a standard deviation of 100.
1.(5) Calculate the probability that a randomly selected student has a SAT score greater than 1650.
2.(5) Calculate the probability that a randomly selected student has a SAT score between 1400 and 1650, inclusive.
3.(5) If we have random sample of 100 students, find the probability that the mean scores between 1485 and 1510, inclusive.
Solution :
1.
P(x > 1650) = 1 - P(x < 1650)
= 1 - P[(x - ) / < (1650 - 1500) / 100)
= 1 - P(z < 1.5)
= 1 - 0.9332
= 0.0668
Probability = 0.0668
2.
P(1400 < x < 1650) = P[(1400 - 1500)/ 100) < (x - ) / < (1650 - 1500) / 100) ]
= P(-1 < z < 1.5)
= P(z < 1.5) - P(z < -1)
= 0.9332 - 0.1587
= 0.7745
Probability = 0.7745
3.
= / n = 100 / 100 = 10
= P[(1485 - 1500) / 10 < ( - ) / < (1510 - 1500) / 10)]
= P(-1.5 < Z < 1)
= P(Z < 1) - P(Z < -1.5)
= 0.8413 - 0.0668
= 0.7745
Probability = 0.7745