Solution :
Given that,
mean =
= unknown
standard deviation =
= 12
n = 36
=
= unknown
=
/
n = 12/
36 = 2
±
5
P(<
< )
= P[ -5 /2 < (
-
)
/
< 5 /2 )]
= P(-2.5 < Z < 2.5)
= P(Z < 2.5) - P(Z < -2.5)
Using z table,
= 0.9938 - 0.0062
= 0.9876
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