18) we know that if X~N(μ, σ^2) ==> (X-μ)/σ ~ N(0,1) or Φ
P(X<30) = P( ((X-46)/20) < ((30-46)/20) )
= P( ((X-46)/20) < (-0.8) )
= Φ (-0.8)
= 1- Φ (0.8) (see graph of standard normal)
= 1- 0.788
= 0.212
option (a)
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"You don't have to believe in God, but you should believe in The Book." -Paul Erdős