Posted by Anonymous on Tuesday, March 20, 2012 at 8:07pm.
μ=50, σ=10;
For score 70, convert to standardized value
z=(x-μ)/σ=(70-50)/10=2
P(x>70)=P(z>2)
Look up standard normal distribution table to get
P(z<=2)=0.9772, so
P(x>70)=P(z>2)=1-0.9772=0.0228
or the average number of students with score of 70 or more
= P(x>70)*200=4.56 = 5 approx.
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