Solution:
n = 55
= 310
s = 75
( a )
z = 1.96
95% confidence interval = 310 1.96 (75/)
= 310 19.8214
= ( 290.1786 , 329.8214 )
( b )
margin of error = 1.96 (75/)
= 19.8214
( c )
ME = 25
we know that
ME = z ( s / )
25 = 1.96 ( 75 / )
= 1.96*75/25
= 5.88
n = 34.57
n 35
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