CBSE 11th Standard Maths Subject Probability Ncert Exemplar 2 Marks Questions With Solution 2021
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CBSE 11th Standard Maths Subject Probability Ncert Exemplar 2 Marks Questions With Solution 2021
11th Standard CBSE
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Reg.No. :
Mathematics
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Suppose that each child born is equally likely to be a boy or a girl. Consider a family with exactly three children.
List the eight elements in the sample space whose outcomes are all possible genders of the three children.(a) -
A and B are two events that P(A) = 0.54, P(B) = 0.69 and \(P(A\cap B)\) = 0.35. Find \(P(B\cap A')\)
(a) -
The probability that at least one of the events A and B occurs is 0.6. If A and B occurs simultaneously with probability 0.2, then find \(P(\overline { A } )+P(\overline { B } ).\)
(a) -
One urn contains two black balls (labelled B1 and B2) and one white (W) ball. A second urn contains one black (B) ball and two white balls (labelled W1 and W2 ). Suppose the following experiment is performed.
One of the two urns is chosen at random. Next , a ball is randomly chosen from the urn. Then, a second ball is chosen at random from the same urn without replacing the first ball. What is the probability that two balls of opposite colour are chosen?(a) -
If A and B are two events having \(P(A\cup B)=\frac { 1 }{ 2 } \ and\ P(\overline { A } )=\frac { 2 }{ 3 } ,\ then\ find\ P(\overline { A } \cap B).\)
(a) -
While suffling a pack of 52 playing cards, 2 are accidentally dropped. Find the probability that the missing cards to be of different colours.
(a) -
If the letters of the word ALGORITHM are arranged at random in a row, what is the probability the letters GOR must remain together as a unit?
(a) -
A single letter is selected at random from the word 'PROBABILITY', then find the probability that letter is vowel.
(a) -
Three digit numbers are formed using the digits 0,2,4,6,8.A number is chosen at random out of these numbers.What is the probability that this number has the same digits?
(a) -
A card is drawn from a deck of 52 cards. Find the probability of getting a king or a heart or a red card.
(a)
2 Marks
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CBSE 11th Standard Maths Subject Probability Ncert Exemplar 2 Marks Questions With Solution 2021 Answer Keys
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Let B denotes a boy and G denotes a girl. Then, all possible genders are expressed as
S={BBB,BBG,BGB,GBB,BGG,GBG,GGB,GGG} -
\(P(B\cap A')=P(B)-P(A\cap B)=0.69-0.35=0.34\)
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We have, \(P(A\cup B)\) = 0.6 and \(P(A\cap B)\) = 0.2
We know, \(P(A\cup B)\) = P(A) + P(B) -\(P(A\cap B)\)
\(\therefore \) 0.6 = P(A) + P(B) - 0.2
P(A) + P(B) = 0.6 + 0.2 = 0.8 ...(i)
Now,
\(P(\overline { A } )+P(\overline { B } )\)
= P(A) +1-P(B)
= 2 - (P(A) + P(B))
= 2 - 0.8
= 1.2 -
Clearly, the sample space of the experiment is
S= {B1B2, B1W, B2B1, B2W, WB1, WB2, BW1, BW2, W1B, W1W2, W2B, W2W1}
Let E be the event that balls of opposite colour are chosen, then
E={B1W, WB1, B2W, WB2, BW1, BW2, W1B, W2B}
\(\therefore \) \(P({ E })=\frac { 8 }{ 12 } =\frac { 2 }{ 3 } \quad \quad \) -
\(We\ have,\ P(A\cup B)=\frac { 1 }{ 2 } \ and\ P(\overline { A } )=\frac { 2 }{ 3 } \)
\(\Rightarrow 1-P(A)=\frac { 2 }{ 3 } \)
\(\Rightarrow P(A)=1-\frac { 2 }{ 3 } =\frac { 1 }{ 3 } \)
\(Also,\ we\ have\ P(A\cup B)=P(A)+P(B)-P(A\cap B)\)
\(\Rightarrow \frac { 1 }{ 2 } =\frac { 1 }{ 3 } +P(B\cap \overline { A } )\)
\(\Rightarrow P(B\cap \overline { A } )=\frac { 1 }{ 2 } -\frac { 1 }{ 3 } =\frac { 1 }{ 6 } \) -
Probability that the missing cards to be different colours
\(=\frac { ^{ 26 }C_{ 1 }\times ^{ 26 }C_{ 1 }\quad }{ ^{ 52 }C_{ 2 } } \)
[in a pack of cards, there are two colours,each of them contain 26 cards]
\(=\frac { 26\times 26\quad }{ \frac { 52\times 51 }{ 2\times 1 } } =\frac { 26 }{ 51 } \) -
There are 9 letters in the word 'ALGORITHM'
These 9 letters can be arranged in a row in 9! ways
\(\therefore\) Total number of possible outcomes = 9!
Now, if the letters GOR remain together, then we have 7 letters (considering GOR as 1 letter i.e. ALITHMGOR)
which can be arranged in 7!
Number of favourable outcomes = 7!
Hence, required probability = \(\frac { 7! }{ 9! } =\frac { 1 }{ 9\times 8 } =\frac { 1 }{ 72 } \) -
There are 11 letters in the word PROBABILITY.
Since, a letter is selected randomly, therefore the possible outcomes are P, R, O, B, A, I, L, T, Y.
But here, outcomes are not equally likely
as P(letter P) = \(\frac { 1 }{ 11 } ;\) P (letter R) = \(\frac { 1 }{ 11 } \)
P(letter O)= \(\frac { 1 }{ 11 } ;\) P (letter B) = \(\frac { 2 }{ 11 } \)
[\(\because \) B repeated twice in the word]
P(letter A) = \(\frac { 1 }{ 11 } ;\) P(letter I) = \(\frac { 2 }{ 11 } \)
P(letter L) = \(\frac { 1 }{ 11 } ;\) P(letter T) = \(\frac { 1 }{ 11 } \)
and P(letter Y) = \(\frac { 1 }{ 11 } \)
Now, let E be event of getting a vowel. Then outcomes favourable to E are A, I and O.
\(\Rightarrow \) E={A,I,O}
Now,\(P(E)=P(A)+P(I)+P(O)\)
[by aximatixc approach to probability]
= \(\frac { 1 }{ 11 } +\frac { 2 }{ 11 } +\frac { 1 }{ 11 } =\frac { 4 }{ 11 } \) -
Since a 3digit number cannot start with 0, therefore hundredth place can be filled up in 4 ways.
Now as repetition of digits is allowed, therefore each of ten's and unit's place can be filled in 5 ways.
Thus , the total number of possible3 -digit number
= 4 x 5 x 5 = 100
Note that, there are three digits numbers, which has the same digits viz. 222,444,666 and 888
\(\Rightarrow \) Number of favourable outcomes = 4
Hence ,P (3digit number with same digits) = \(\frac { 4 }{ 100 } =\frac { 1 }{ 25 } \) -
Let S be the sample space. Then, n(s) = 52
Let A, B and C be the event of getting a king, a heart and a red card, respectively.
Then,
\(n(A)=4,n(B)=13,n(C)=26\)
\(\therefore \ P(A)=\frac { n(A) }{ n(S) } =\frac { 4 }{ 52 } =\frac { 1 }{ 13 } \)
\(P(B)=\frac { n(B) }{ n(S) } =\frac { 13 }{ 52 } =\frac { 1 }{ 4 } \)
\(P(C)=\frac { n(C) }{ n(S) } =\frac { 26 }{ 52 } =\frac { 1 }{ 2 } \)
Clearly, \((A\cap B)\) is the event of getting a king among hearts.
\((B\cap C)\) is the event of getting a heart among red cards.
\((A\cap C)\) is the event of getting the king among red cards.
\((A\cap B\cap C)\) is the event of getting a king among heart and the red cards.
\(\Rightarrow n(A\cap B)=1,n(B\cap C)=13,n(A\cap C)=2\ and\ n(A\cap B\cap C)=1\)
\( \therefore \ P(A\cap B)=\frac { n(A\cap B) }{ n(S) } =\frac { 1 }{ 52 } ,\)
\(P(B\cap C)=\frac { n(B\cap C) }{ n(S) } =\frac { 13 }{ 52 } =\frac { 1 }{ 4 }\)
\(P(A\cap C)=\frac { n(A\cap C) }{ n(S) } =\frac { 2 }{ 52 } =\frac { 1 }{ 26 } \)
\(and\ P(A\cap B\cap C)=\frac { n(A\cap B\cap C) }{ n(S) } =\frac { 1 }{ 52 } \)
\(Now,\ P(getting\ a\ king\ or\ heart\ or\ red\ card)\)
\( =P(AorBorC)=P(A\cup B\cup C)\)}
\(=P(A)+P(B)+P(C)-P(A\cap B)-P(A\cap C)-P(B\cap C)+P(A\cap B\cap C)\)
\(=\frac { 1 }{ 13 } +\frac { 1 }{ 4 } +\frac { 1 }{ 2 } -\frac { 1 }{ 52 } -\frac { 1 }{ 26 } -\frac { 1 }{ 4 } +\frac { 1 }{ 52 } =\frac { 28 }{ 52 } =\frac { 7 }{ 13 } \)
2 Marks