i) In an open exanination, the average for a subject is 75, with a
standard of deviation of 8, the grades distribution follows a
normal distribution pattern. Determine the minimun mark for
Grade A for this subject if 15% of the students are given A's
ii) Three fair coins are tossed in an experiment
a) Find the probability of getting at least one head
b) Find the probability of getting exactly two head
Standard Distribution
2009-03-26 10:23 pm
回答 (1)
2009-03-26 10:52 pm
✔ 最佳答案
i. Let X be the mark got in the examination.Let C be the minimum mark required to get an A.
X ~ N(75, 82)
P(get A) = 15%
P(z > (C - 75)/8) = 0.15
(C - 75)/8 = 1.036521739
C = 83.3 (1 d.p.)
The minimum mark required is 83.3.
ii.a. P(at least one head)
= 1 - P(no head)
= 1 - P(3 tails)
= 1 - (1/2)3
= 7/8
b. P(exactly two heads)
= P(two heads and one tail)
= 3C2 X (1/2)2 X (1/2)
= 3/8
參考: Physics king
收錄日期: 2021-04-19 14:05:39
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