The value of the mean for the scores in an exam which are normally distributed is 70.
Given:
the scores in an exam were normally distributed with unknown mean and a standard deviation of 5 .
if 30.85 % of students scored more than 72.5 . what is the value of the mean = ?
Mean = µ
σ = 5
x = 72.5
The z score corresponding to the area 30.85% in the right tail is :
Zi score = Z 0.3085
= 0.500
Again : Z₀ = x- µ/σ
⇒ x- µ = Z₀σ
⇒ µ = x - Z₀σ
= 72.5 - 0.500 × 5 (using z table)
= 72.5 - 2.5
= 70
Hence we get the unknown mean as 70.
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