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NCERT Class XII Mathematics Chapter - - Solutions

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Question : 88
Total: 101
In a hurdle race, a player has to cross 10 hurdles. The probability that he will clear each hurdle is
5
6
. What is the probability that he will knock down fewer than 2 hurdles ?
Solution:  
We have , p = probability that clears the hurdle =
5
6
,
q = probability that he does not clears the hurdle =1−
5
6
 and n=10.
∴ Required probability = P(knocking down fewer than 2 hurdles)
= P(he will cross all hurdles) + P(he will not cross 1 hurdle)
=(
5
6
)10+10(
5
6
)9(
1
6
)
=(
5
6
)9[
5
6
+
10
6
]=
510
2×69
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