Method 1: (50, 100) is (μ, σ? ), μ=50 is the mean, σ? = 100 is the variance.

According to the formula: p (x ≤ 40) = p (x-μ/σ≤ 40-μ/σ) = p (x-μ/σ≤1), we can look up the normal distribution table and get the result of 0. 1587.

Method 2: p (σ) = p (u-σ

P(X≤40)=？ [ 1-P(50- 10 & lt； X≤50+ 10)]=？ ( 1-0.6826)=0. 1587.

Extended data?

Normal distribution: IQ, grades, product quality, height, etc. All conform to the normal distribution law. Normal distribution means that the middle is high and the two sides are low, and big data is distributed in the middle.