In a packet of 50 screws 8 per cent are defective screws. 3 screws are taken at random from the packet. Find the probability that (i) all screws are non-defectives (ii) 1 screw is defective.
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machine manufactures 5% defective screws. Probability of defective screws =
100
5
=
20
1
In sample of 15 screws; n=15
Probability that there are exactly 3 defectives =
n
C
k
p
k
(1−p)
n−k
=
15
C
3
(
20
1
)
3
(1−
20
1
)
15−3
=
15
C
3
(
20
1
)
3
(
20
19
)
12
Answered by
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Answer:
No. of defective screws= 8/100*50=4
i) Applying the formula, 1419/1960 is our result.
ii) (9/10)^3
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