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Published on: 16/09/2019
Probability
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1.
1000 tickets of a lottery were sold and there are 5 prizes on these tickets. If John has purchased one lottery ticket, what is the probability of winning a prize?
2.
A coin is tossed two times. Find the probability of getting at least one head.
3.
At a fete, cards bearing numbers 1 to 1000, one number on one card, are put in a box. Each player select one card at random and that card is not replaced. If the selected card has a perfect square greater than 500, the player wins a prize. What is the probability that
(i) the first player wins a prize?
(ii) the second player wins a prize, if the first has won?
4.
A bag contains 5 red balls, 8 white balls, 4 green balls and 7 black balls. If one ball is drawn at random, find the probability that it is (i) black (ii) red (iii) not green.
5.
The king, queen and jack of clubs are removed from a deck of 52 playing cards and the remaining cards are shuffled. A card is drawn from the remaining cards. Find the probability of getting a card of
(i) heart
(ii) queen
(iii) clubs
6.
Find the probability that a leap year should have exactly 52 tuesday.
7.
A letter of English alphabet is chosen at random. Determine the probability that the letter is a Consonant.
8.
A die is thrown once. What is the probability of getting a number greater than 4?
9.
A man is known to speak truth 5 out of 7 times. He throws a die and a number other than six comes up. Find the probability that he reports it is a six.
10.
A pair of dice is thrown once. Find the probability of getting the same number on each dice.
11.
It is given that in a group of 3 students, the probability of 2 students not having the same birthday is 0.992. What is the probability that the 2 students have the same birthday?
12.
Why is tossing a coin considered to be a fair way of deciding which team should get the ball at the beginning of a football game?
13.
A die is thrown twice. What is the probability that
(i) 5 will not come up either time?
(ii) 5 will come up at least once?
[Hint : Throwing a die twice and throwing two dice simultaneously are treated as the same experiment]
14.
A die is thrown once. Find the probability of getting
(i) a prime number.
(ii) a number lying between 2 and 6.
(iii) an odd number
15.
A box contains 90 discs which are numbered from 1 to 90. If one disc is drawn at random from the box, find the probability that is bears
(i) a two digit number
(ii) a perfect square number
(iii) a number divisible by 5
1.
Total number of tickets 1000, Number tickets with prizes = 5
\(\therefore\) Probability of winning a prize = \(\frac{5}{1000}\)
= 0.005
2.
Possible outcomes are HH, HT, TH, TT
\(\Rightarrow\) Number of total outcomes = 4
Let A = Atleast one head
Favourable outcomes of event A are HH, HT or TH
\(\therefore\) Number of favourable outcomes = 3
P(A) = \(\frac{3}{4}\)
3.
Number of ways to draw a card by 1st player = 1000
perfect square greater than 500 are 529, 576, 625, 676, 729, 784, 841, 900, 961
\(\therefore \)Probability of 1st player winning the prize = \(\frac { 9 }{ 1000 } \)
when 1st has won the prize then cards left = 999 (because card is not replaced)
Cards with no. which a perfect square greater than 500 = 8 (l winning number removed)
\(\therefore \)Probability of second player wins a prize when the first player has won =\(\frac { 8 }{ 999 } \)
4.
Total balls in the bag = 5 + 8 + 4 + 7 = 24
(i) Number of black balls = 7. So Probability drawing a black ball =\(\frac { 7 }{ 24 } \)
(ii) Number of red balls = 5 So Probability of drawing a red ball =\(\frac { 5 }{ 24 } \)
(iii) Number of balls which are not green = Number of red balls + Number of white + Number of black balls = 5+8+7=20
\(\therefore \)Probability of drawing a ball which is not green is \(\frac { 20 }{ 24 } =\frac { 5 }{ 6 } \)
5.
Given that king, queen and jack of club are removed from a pack then number of remaining cards 49
(i) then probability of getting a heart = \(\frac{13}{49}\)
(ii) probability of getting a queen = \(\frac{3}{49}\)
(iii) probability of getting a club = \(\frac{10}{49}\)
6.
Number of days in a leap years = 366, Number of weeks = 52
\(\therefore \) Number of tuesdays in 52 weeks = 52
Number of days left after 52 weeks = 366-52 x 7 = 2.
Now, exactly 52 tuesday mean there should not be a tuesday in the remaining 2 days
Possible outcome of remaing two days (Monday, Tuesday), (Tuesday, Wednesday), (Wednesday, Thursday), (Thursday, Friday), (Friday, Saturday), (Saturday, Sunday) or (Sunday, Monday)
Total possible outcome = 7
Probability of not getting a Tuesday = \(\frac { 5 }{ 7 } \)
\(\therefore \)Probability of getting exactly 52 Tuesday= \(\frac { 5 }{ 7 } \)
7.
We know that in English alphabet, there are 26 letters (5 vowels + 21 consonants).
So, total number of outcomes = 26
Let E be the event of choosing a consonant.
\(\therefore\) Number of outcomes favourable to E = 21
Hence, required probability = \(P(E)=\frac{21}{26}\)
8.
Total possibilities = 6 and favourable possibilities for number greater than 4 are 2 (i.e. 5, 6).
\(\therefore\) Probability of getting a number greater than 4 = \(\frac{2}{6}=\frac{1}{3}\)
9.
P(man will speak the truth) = \(\frac { 5 }{ 7 } \)
P(man will not speak the truth)
= \(1-\frac { 5 }{ 7 } =\frac { 2 }{ 7 } \)
when a number other than 6 comes up the probability of man's reporting it is a six is the probability of man's not speaking the truth = \(\frac { 2 }{ 7 } \)
10.
Total number of ways to throw a pair of dice = 36
Same number on each dice, i.e. (1,1), (2,2), (3,3), (4,4), (5,5), (6,6)
\(\therefore\) Number of ways of getting the same number on each dice = 6
Required probability = \(\frac{6}{36}=\frac{1}{6}\)
11.
We have P(E) + P(not E) = 1
P(E) + 0.992 = 1
P(E) = 1 - 0.992 = 0.008
12.
When we toss a coin,we get either head or tail which are equally likely outcomes. Hence, the result of the toss of a coin is completely unpredictable or unbiased. So, tossing a coin is a fair way of deciding.
13.
Total number of outcomes = 36
(i) Let E = Event of getting 5 on atleast one die
Then, E would consist of 11 outcomes, namely (1,5), (2, 5), (3, 5), (4, 5), (5, 5), (6, 6), (5, 1), (5, 2), (5, 3), (5, 4) and (5, 6).
\(\therefore\) Number of outcomes favourable to E = 11
Hence, probability that 5 will come up atleast once,
\(P(E)=\frac{11}{36}\)
(ii) Probability that 5 will not come up either time,
\(P(\bar{E})=1-P(E)=1-\frac{11}{36}=\frac{25}{36}\)
14.
On a die, there are six numbers 1, 2, 3, 4, 5 and 6.
\(\therefore\) Total number of possible outcomes =6
(i) Let E1 = Event of getting a prime number
Then, E1 would consist of three outcomes namely 2, 3 and 5.
\(\therefore\)Number of outcomes favourable to E1 = 3
Probability of getting a prime number,
\(P\left(E_1\right)=\frac{3}{6}=\frac{1}{2}\)
(ii) Let E2 = Event of getting a number lying between 2 and 6
Then, E2 would consist of three outcomes, namely 3, 4 and 5.
\(\therefore\) Number of outcomes favourable to E2 = 3
Probability of getting a number lying between 2 and 6,
\(P\left(E_2\right)=\frac{3}{6}=\frac{1}{2}\)
(iii) Odd numbers = 1, 3, 5
\(\therefore\) P(an odd number) = \(\frac{3}{6}=\frac{1}{2}\)
15.
(i) Total number of discs in a box = 90
\(\therefore\) Number of all possible outcomes = 90
Let E1 = Event of getting a disc bearing a two-digit number
Here, two-digit numbers are 10, 11, .., 90
\(\therefore\)Number of outcomes favourable to E1 =81
Hence, probability of getting a disc bearing a two-digit number, \(P\left(E_1\right)=\frac{81}{90}=\frac{9}{10}\)
(ii) Let E2 = Event of getting a disc bearing a perfect square number
Here, perfect square number are 1, 4, 9, 16, 25, 36, 49, 64 and 81.
\(\therefore\) Number of outcomes favourable to E2 =9
Hence, probability of getting a disc bearing a perfect square number, \(P\left(E_2\right)=\frac{9}{90}=\frac{1}{10}\)
(iii) Let E3 = Event of getting a disc bearing a number divisible by 5
Here, the numbers divisible by 5 are
5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 and 90
\(\therefore\) Number of outcomes favourable to E3 = 18
Hence, required probability = \(P\left(E_3\right)=\frac{18}{90}=\frac{1}{5}\)
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