Ask a college probability question

Let the test score be x, then X ~ n (μ, σ 2), then (X-μ)/σ~N(0, 1).

According to the question p (x > 90)= 12/526, so p [(x-μ)/σ >; (90-μ)/σ]= 12/526

Lookup table (90μ)/σ= 2

According to the meaning of question p (x)

Look-up table (60 μ)/σ =-1.

The solution is μ=70, σ= 10.

p(X & lt； 78)= P[(X-70)/ 10 & lt； (78-70)/ 10]=Φ(0.8)=0.788 1

p(X & gt； 78)=0.2 1 19

526*0.2 1 19= 1 1 1

That is to say, only11people with higher grades can be admitted.