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Published on: 26/09/2019
Probability
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1.
A group consists of 12 persons, out of which 3 are extremely patient, other 6 are extremely honest and rest are extremely kind. A person from the group is selected at random. Assuming that each person is equally likely to be selected, find the probability of selecting a person who is
(i) extremely kind or honest
(ii) Which of the above values you prefer more?
2.
All the three face cards of spades are removed from a well-shuffled pack of 52 cards. A card is then drawn at random from the remaining pack. Find the probability of getting
(i) a spade
3.
Two unbiased coins are tossed simultaneously. find the probability of getting
(i) no heads
(ii) atmost one tail
(iii) one tail
(iv) one head and one tail
4.
A box of 24 solar cells contain 8 defective cells.One cell is drawn at random.What is the probability that the cell is not defective and it is not replaced and a second cell is selected at random from the rest, what is the probability that second cell is defective?
5.
Two dice are numbered 1,2,3,4,5,6 and 1,1,2,2,3,3 respectively.They are thrown and the sum of the numbers on them is noted.Find the probability of getting each sum from 2 to 9 separately
6.
At a fete cards bearing numbers 1 to 500, one on each card, are put in a box. Each player selects one card at random and that card is not replaced. If the selected card bears a number which is a perfect square of an even number the player wins prize.
(i) What is the probability that the first player wins a prize?
(ii) The second player wins prize, if the first has not won.
7.
A coin is tossed. If it results in a head a coin is tossed, otherwise a die is thrown. Describe the following events:
(i) A = getting atleast one head
(ii) B = getting an even number
(iii) C = getting a tail
(iv) D = getting a tail and an odd number
8.
In a game, the entry fee is Rs. 5. The game consists of tossing a coin 3 times. If one or two heads show, then Sweta gets her entry fee back. If she tosses 3 heads, then she receives double the entry fees. Otherwise she will lose. For tossing a coin three times, find the probability that she
(i) loses the entry fee
(ii) gets double entry fee
(iii) just gets her entry fee
9.
Two dice are numbered 1, 2, 3, 4, 5, 6 and 1, 2, 2 3, 3, 4 respectively. They are thrown and the sum of the numbers on them is noted. Find the probability of getting (i) sum 7 (ii) sum is a perfect square.
1.
Given, a group consists 12 persons.
\(\therefore \) Total number of outcomes = 12
(i) Given, number of extremely patient persons = 3
\(\therefore \) Number of favourable outcomes = 3
\(\therefore \) P (extremely patient) = \(\frac{3}{12} = \frac{1}{4}\)
(ii) Given, number of extremely honest persons = 6 and number of extremely kind persons
= 12 - 6 - 3 = 3
\(\therefore \) Number of favourable outcomes = Number of extremely kind persons + Number of extremely honest persons = 6 + 3 = 9
\(\therefore \) P (extremely kind or honest) = \(\frac{9}{12}=\frac{3}{4}\)
2.
Remaining cards of spade=13-3=10
So, favourable outcomes=10,
i.e. n(E4)=10
∴ P(getting a spade)\(=\frac { 10 }{ 49 } \)
3.
When two coins are tossed simultaneously, all possible outcomes are {HH, HT, TH, TT}.
Total number of sample space is n(S)=4
(i) Let E1=Event of getting no head={TT}
n(E1)=1
∴ P (getting no head)\(=\frac { n(E_{ 1 }) }{ n(S) } =\frac { 1 }{ 4 } \)
(ii) Let E2=Event of getting at most one tail
={HT, TH, HH}
n(E2)=3
∴ P (getting atmost one tail)\(=\frac { n(E_{ 2 }) }{ n(S) } =\frac { 3 }{ 4 } \)
(iii) Let E2=Event of getting one tail={HT, TH}
n(E3)=2
∴ P (getting one tail)\(=\frac { n(E_{ 3 }) }{ n(S) } =\frac { 2 }{ 3 } =\frac { 1 }{ 2 }\)
(d) Let E4=Event of getting one head and one tail
={HT, TH}
n(E4)=2
∴ P (getting one head and one tail)\(=\frac { n(E_{ 4 }) }{ n(S) } =\frac { 2 }{ 4 } =\frac { 1 }{ 2 }\)
4.
\({2\over3},{8\over23}\)
5.
When two dice are thrown simultaneously, then sample space contain ( 6 X6=36) outcomes
Sum 2 i.e., [(1,1),(1,1)] = two outcomes
P( Sum 2) = 2 / 36 = 1 / 18
Sum 3 i.e., (1,2), (1,2), (2,1), (2,1) =4 outcomes.
P( Sum 3) = 4 / 36 = 1 / 9
Sum 4 i.e., [(1,3), (1,3), (2,2), (2,2),(3,1), (3,1)] =6 outcomes
P( Sum 4) = 6 / 36 = 1 / 6
Sum 5 i.e., [(2,3), (2,3), (3,2), (3,2),(4,1), (4,1)] =6 outcomes
P( Sum 5) = 6 / 36 = 1 / 6
Sum 6 i.e., [(3,3), (3,3), (4,2), (4,2),(5,1), (5,1)] =6 outcomes
P( Sum 6) = 6 / 36 = 1 / 6
Sum 7 i.e., [(4,3), (4,3), (5,2), (5,2),(6,1), (6,1)] =6 outcomes
P( Sum 7) = 6 / 36 = 1 / 6
Sum 8 i.e., [(5,3), (5,3), (6,2), (6,2)] =4 outcomes
P( Sum 8) = 4 / 36 = 1 / 9
Sum 9 i.e., [(6,3), (6,3)] =2 outcomes.
P( Sum 9) = 2 / 36 = 1 / 18
6.
(i)There are 500 possible ways to draw a card.Perfect squares of even numbers are 4, 16, 36, 64, 64, 100, 144,196, 256, 324, 400, 484.
Number of ways to draw a no. of which is a perfect square of even number =11
Probability of first player winning a prize = \(11\over 500\)
(ii)For second players No. of cards left = 500-1=499
[∵ One card has been drawn by 1st players and it has not been replaced]
Also No. of cards bearing perfect square of even number = 11
[∵ 1st players has not won ∴ Card drawn by him does not bear a perfect square even numbert]
∴ Probability of IInd player winning a prize = \(11\over 499\)
7.
Total outcomes
(H, H), (H, T), (T, 1), (T, 3), (T, 4), (T, 5), (T, 6)
A=(H, H), (H, T)
B=(T, 2), (T, 4), (T, 6)
C=(H, T), (T, 1), (T, 2), (T, 3), (T, 4), (T, 5), (T, 6)
D=(T, 1), (T, 3), (T, 5)
8.
Possible outcomes on tossing a coin 3 times, are HHH, HHT, HTH, THH, HTT, THT, TTH, TTT
\(\therefore\) Total number of outcomes = 8
(i) Let E1 be the event that Sweta losses the entry fee
i.e. shen tosses tail three times i.e. TTT.
\(\therefore\) Number of outcomes favourable to E1 = 1
Hence, required probability = P(E1) = \(\frac{1}{8}\)
(ii) Let E2, be the event that Sweta gets double entry fee
i.e. she tosses heads three times
i.e. HHH
\(\therefore\) Number of outcomes favourable to E2 = 1
Hence, required probability \(=P\left(E_2\right)=\frac{1}{8}\)
(iii) Let E3 be the event that Sweta gets her entry fee back
i.e. Sweta gets heads one or two times
i.e. event of getting
HTT, THT, TTH, HHT, HTH or THH
\(\therefore\) Number of outcomes favourable to E3 = 6
Hence, required probability = P(E3) = \(\frac{6}{8}=\frac{3}{4}\)
9.
When these dice are thrown then total possible outcomes are
\(\therefore\)Total possible outcomes = 36
(i)Sum of number = 7
Favourable outcomes are (3,4), (4, 3), (4, 3), (5, 2), (5,2), (6,1)
\(\therefore\)Favourable wavs = 6
\(\therefore\)Probability that sum of number is 7 = \(\frac{6}{36}=\frac{1}{6}\)
(ii)Sum is a perfect square i.e., sum is 4 or 9 (\(\therefore\)Maximum sum is 10)
Favoutable outcomes are (1, 3), ( 1, 3), (2, 2), (2, 2), (3, 4), (6, 3), (6, 3) = 7 outcomes.
\(\therefore\)Probability = \(\frac {7}{36}\)
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