Let X= the number of weeks in which the value of US dollar rising against the Japanese yen: X∼Bin(n,p)
P(X=x)=(xn)px(1−p)n−x Given n=7,p=0.5
P(X≥4)=P(X=4)+P(X=5)+P(X=6)+
+P(X=7)=(47)0.54(1−0.5)7−4+(57)0.55(1−0.5)7−5+
+(67)0.56(1−0.5)7−6+(77)0.57(1−0.5)7−7=
=1281(35+21+7+1)=0.5
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