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JEE Main Math Class 12 Probability Part 1 Questions
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© examsnet.com
Question : 13
Total: 100
Box I contains 30 cards numbered 1 to 30 and Box II contains 20 cards numbered 31 to 50. A box is selected at random and a card is drawn from it. The number on the card is found to be a non-prime number. The probability that the card was drawn from Box I is :
[Sep. 02, 2020 (I)]
2
3
8
17
4
17
2
5
Validate
Solution:
Let
B
1
and
B
2
be the boxes and
N
be the number of non-prime number.
∵
P
(
B
1
)
=
P
(
B
2
)
=
1
2
and
P
(non-prime number)
=
P
(
B
1
)
×
P
(
N
B
1
)
+
P
(
B
2
)
×
P
(
N
B
2
)
=
1
2
×
20
30
+
1
2
×
15
20
So,
P
(
B
1
N
)
=
P
(
B
1
)
×
P
(
N
B
1
)
P
(
B
1
)
×
P
(
N
B
1
)
+
P
(
B
2
)
×
P
(
N
B
2
)
=
1
2
×
20
30
1
2
×
20
30
+
1
2
×
15
20
=
1
3
1
3
+
15
40
=
8
17
© examsnet.com
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