Let X= student's mark: X∼N(μ,σ)
P(X<x1)=P(Z<σx1−μ)=0.07
P(X<x2)=P(Z<σx2−μ)=0.89
σx1−μ≈−1.475791
σx2−μ≈1.226528
x1=0.35,σ0.35−μ≈−1.475791
x2=0.6,σ0.6−μ≈1.226528
μ=0.35+1.475791σ
μ=0.6−1.226528σ
0.35+1.475791σ=0.6−1.226528σ
σ=1.475791+1.2265280.6−0.35≈0.0925
μ≈0.4865
μ=48.65%,σ=9.25%
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