In an examination ,student A's result was 1.6 standard deviations above the mean and student B's result was 0.4 standard deviations below the mean. Student C got 60 marks which was 0.2 standard deviation below the mean . Given that student A got 30 marks more than student B in the examinaton ,find
(a)the standard deviation of the the marks of marks of the whole class,
(b)the mean mark of the whole class,
(c)the results of student A and B.
answers:(a)15 (b)63 (c)A:87 B:57
standard deviation
2007-06-06 1:16 am
回答 (2)
2007-06-06 1:31 am
✔ 最佳答案
Let m = mean mark of the whole class and s= standard deviation.
Therefore
A's result = m + 1.6s
B's result = m - 0.4s
C's result= m - 0.2s =60 Eq. 1
Since A got 30 marks above B
m +1.6s = m - 0.4s + 30
or 2s = 30 or s =15. Answer a) s = 15
Subsititute s to Eq. 1
m - 3 = 60
Therefore m = 63 Answer (b) m = 63
With these info
A's mark = 63 + 1.6*15 = 87
B's mark = 87 - 30 = 57
2007-06-07 1:36 am
let the mean=x
standard deviation=y
x-0.2y=60
(x+1.6y)-(x-0.4y)=30
2y=30
a)y=15
x-0.2(15)=60
b)x=63
c)A:63+1.6x15=87
B:63-0.4x15=57
standard deviation=y
x-0.2y=60
(x+1.6y)-(x-0.4y)=30
2y=30
a)y=15
x-0.2(15)=60
b)x=63
c)A:63+1.6x15=87
B:63-0.4x15=57
參考: me
收錄日期: 2021-04-12 19:53:04
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