a)
Concrete blocks are tested and it is found that, on average, 7% fail to meet the required specification. To pick up 9 concrete blocks from a batch of concrete blocks in a construction site, determine the probabilities that less than three blocks out from the chosen 9 concrete blocks will fail to meet the specification.
Let N = no. of concrete blocks that fail from a batch of 9 concrete blocks
P (less than 3 blocks fail)
= P(N=0) + P(N=1) + P(N=2)
= (1-0.07)^9 + (9C1) (1-0.07)^(8) (0.07) + (9C2) (1-0.07)^7(0.07)^2
=0.9791
咁樣岩唔岩？ thanks a lot!
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本帖最後由 Methodical 於 2016-9-21 03:58 PM 編輯 ]
