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Joint Entrance Examination
Mathematics
Probability
Question 239
Question 239 of 417
Medium
MCQ
P, Q, R try to hit a target independently with probabilities
3
4
,
1
2
,
5
8
\dfrac34,\dfrac12,\dfrac58
4
3
,
2
1
,
8
5
. Find the probability the target is hit by P or Q but not R.
A
21
/
64
21/64
21/64
B
9
/
64
9/64
9/64
C
15
/
64
15/64
15/64
D
39
/
64
39/64
39/64
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Official solution
\[P = [P(P)+P(Q)-P(P)P(Q)]\times(1-P(R)) = \left(\frac34+\frac12-\frac38\right)\times\frac38 = \frac78\times\frac38=\frac{21}{64}\]
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