data groupA: 40 students, mean mark=50, standard deviation=15
data groupB: 40 students, mean mark= 40,standard deviation=10
if data group A is combined with data group B, what's the new mean and standard deviation?explain
standard deviation
2009-12-01 4:54 am
回答 (1)
2009-12-01 5:05 am
✔ 最佳答案
Total mark of group A = 40 X 50 = 2000Total mark of group B = 40 X 40 = 1600
Total mark of the two groups, u = 2000 + 1600 = 3600
So, the new mean = total mark of the two groups / Total number of people
= 3600 / (40 + 40)
= 45
New variance
= [40/(40 + 40)](50^2 + 15^2) + [40/(40 + 40)](40^2 + 10^2) - 45^2
= 187.5
So, the new standard deviation
= sqrt(187.5)
= 13.6931 (4 d.p.)
參考: Physics king
收錄日期: 2021-04-19 20:44:38
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20091130000051KK01414