간단한 통계 문제좀 알려주실분 ㅜㅜ

If a data has a mean of 20.0 and a standard deviation of 3.0, which of the
following values is more than 2.5 standard deviations from the mean?
A) 13.5 B) 17.0 C) 23.5 D) 12.0

 

정답 D

What happens to the standard error (SE) of the sample mean when you
increased sample size from 100 to 400?
A) It does not change SE B) It increases SE two times
C) It cuts SE by a half D) It cuts SE 75%

 

정답c

 

You believed that the probability of having a success is less than 0.5. You
tried 20 times; and X=5. What is the p-value?
A) 1 - P(X < 5) B) P(X ≤ 5) + P(X ≥ 15)
C) P(X ≥ 5) D) P(X ≤ 5)

 

정답D

 

Set S has μ = 10 and σ = 1.5. We are going to add two additional
numbers to Set S. Which pair of numbers would decrease the standard
deviation the most?
A) {2, 10} B) {16, 16} C) {9, 11} D) {10, 18}

정답C

 

인데 이유좀 간단하게 설명해주실 분 있으신가요 ㅜㅜ부탁드립니다.