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Published on: 17/10/2019
Probability
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1.
50 plants were sown in fice different colonies A, B, C, D and E. After 30 days, the number of plants survived as follows:
| Colony | A | B | C | D | E |
| No. of plants survivied | 40 | 45 | 42 | 38 | 41 |
What is the probability that:
(i) more than 40 plants survived in a colony?
(ii) less than 41 plants survived in a colony?
(iii) Which values are depicted from above data?
2.
In cricket match, a batsmen hits a boundary 12 times out of 48 balls he plays. Find the probability that he does not hit a boundary in the next ball.
3.
An insurance company selected 2000 drivers a random in a particular city to find a relationship between age and accidents the data obtained are given in the following table?
| Age of drivers (in years) |
Accidents in one year | ||||
| 0 | 1 | 2 | 3 | Over 3 | |
| 18-29 | 440 | 160 | 110 | 61 | 35 |
| 30-50 | 505 | 125 | 60 | 22 | 18 |
| Above 50 | 360 | 45 | 35 | 15 | 9 |
Find the probabilities of the following events for a driver chosen at random from the city:
(i) being 18-29 years of age and having exactly 3 accidents in one year.
(ii) being 30-50 years of age and having one or more accidents in one year.
(iii) having no accidents in one year.
4.
The heights of the students of a class is measured and recorded as given below:
| Height (in cm) | No. of Students |
| 120-125 | 7 |
| 125-130 | 7 |
| 130-135 | 11 |
| 135-140 | 3 |
| 140-145 | 5 |
| 145-150 | 9 |
| 150-155 | 8 |
A student is selected at random. Find the probability that height of the students is :
(i) more than 135 cm
(ii) at least 145 cm
(iiii) less than 130 cm
(iv) 125 cm or more but less than 140 cm
5.
Following table shows the marks scored by a group of students in a mathematics test of 100 marks:
| marks | No. of students |
| 0-20 | 7 |
| 20-30 | 10 |
| 30-40 | 10 |
| 40-50 | 20 |
| 50-60 | 20 |
| 60-70 | 15 |
| 70-80 | 8 |
A student is selected at random. Find the probability that student has obtained.
(i) Less than 30
(ii) 60 or more marks
(iii) between 40 and 70 marks
(iv) 70 or more marks
6.
The king, queen, and jack of clubs are removed from a deck of 52 cards and then shuffled. One card is selected from the remaining cards. What is the probability of getting
(a) a heart
(b) a king
(c) the 10 of hearts.
7.
An insurance company selected 1600 drivers at random in a particular city to find a relationship between age and number of accidents. The data obtained are given in the following table:
| Age of drivers (in years) |
No.of accidents(in one year) | ||||
| 0 | 1 | 2 | 3 | More than 3 | |
| 18-25 | 320 | 125 | 75 | 45 | 30 |
| 25-40 | 400 | 45 | 50 | 15 | 10 |
| 40-55 | 150 | 85 | 13 | 8 | 10 |
| Above 55 | 150 | 25 | 17 | 20 | 7 |
Find the number of drivers
(a) in the age of 25-40 years and has more than 2 accidents in the year.
(b) in the age above 40 years and has accidents more than 1 but less than 3.
8.
At a hospital, a doctor compiled the following data about 400 patients whom he could cure of hepatitis:
| Time for cure | No.of patients |
| <1 month | 210 |
| 1-2 months | 105 |
| 2-3 months | 60 |
| >3 months | 25 |
Another case of hepatitis is reported. What is the probability that this patient will be cured in
(i) less than 2 months?
(ii) 1 month or more but not more than 3 months?
9.
Cards marked with numbers 2 to 101 are placed in a box and mixed thoroughly. One card is drawn from this box. Find the probability that the number on the card is
(a) a number less than 14
(b) a number which is a perfect square
(c) a prime number less than 20
10.
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) not green.
11.
Out of the past 250 consecutive days, its weather forecasts were correct 175 times.
(i) What is the probability that on a given day it was correct?
(ii) What is the probability that it was not correct on a given day?
12.
A survey of 500 families was conducted to know their opinion about a particular detergent powder. If 375 families liked the detergent powder and the remaining families disliked it, find the probability that a family chosen at random
(i) likes the detergent powder
(ii) does not like it.
1.
We have total number of colonies = 5
(i) Number of colonies in which more than 40 plants survived = 3(B,C and E)
\(\therefore \) P(more than 40 plants survived in a colony)\(=\frac{3}{5}\)
(ii) Number of colonies in which less than 41 plants survived = 2(A and D)
P(less than 41 plants survived in colony)\(=\frac{2}{5}\)
(iii) In order to keep environment safe, we should grow more and more plants.
2.
Let E be the event the batsman hits a boundary.
Then \(\overline E\) is the event the batsman does not hit a boundary.
P(E) = \(\frac{12}{48}=\frac{1}{4}\)
\(\Rightarrow P(\overline E)=1-P(E)\)
\(=1-\frac{1}{4}=\frac{3}{4}\)
3.
Total no. of drivers = 2000
(i) Number of drivers who are 18-29 years old and have exactly 3 accidents in one year in 61
So, \(P=\frac{61}{2000}\)
(ii) Number of drivers having 30-50 years of age and having one or more accidents in one year.
= 125 + 60 + 22 + 18
= 225
So, probability, P\(=\frac{225}{2000}=\frac{9}{80}\)
(iii) Number of drivers having no accident in one year = 440 + 505 + 360 = 1305
So, probability P = \(\frac{1305}{2000}=\frac{261}{400}\)
4.
Total student = 7 + 7 + 11 + 3 + 5 + 9 + 8 = 50
(i) P(height of student is more that 135 cm)\(=\frac{25}{50}=\frac{1}{2}\)
(ii)P(height of student is at least 145 cm)\(=\frac{17}{50}\)
(iii) p(height of student is less than 130 cm)\(=\frac{14}{50}=\frac{7}{25}\)
(iv) P(height of student is 125 or more but less than 140)\(=\frac{21}{50}\)
5.
(i) Probability of less than 30 marks\(=\frac{7+10}{=90}=\frac{17}{90}\)
(ii) Probability of marks 60 or more marks\(=\frac{15+8}{90}=\frac{23}{90}\)
(iii) Probability of marks between 40 and 70\(=\frac{20+20+15}{90}\)
\(=\frac{55}{90}\)
(iv) Probability of marks 70 or more \(=\frac{8}{90}=\frac{4}{45}\)
6.
Total number of cards in the deck when king, queen, and jack of clubs are removed
= 52 - 3 = 49
(a) Number of cards which are 'a heart' = 13
Probability of getting a heart = \(\frac { 13 }{ 49 } \)
(b) Number of cards which are 'a king' = 3
Probability of getting a king =\(\frac { 3 }{ 49 } \)
(c) Number of cards which are 'the 10 of hearts' = 1
Probability of getting 'the 10 of hearts' = \(\frac { 1 }{ 49 } \)
7.
(a) The number of drivers in the age of 25-40 years and has more than 2 accidents in the year
= 15 + 10 = 25
(b) The number of drivers the age of whose is above 40 years and has accidents more than 1 but less than 3
= 13 + 17 = 30.
8.
Total number of patients = 400
(i) Number of patients who were cured in less than 2 months = 210 + 105 = 315
Probability that the patient will be cured in less than 2 months\(=\frac { 315 }{ 400 } =\frac { 63 }{ 80 } \)
(ii) Number of patients who were cured in 1 month or more but not more than 3 months
= 105 + 60 = 165
Probability that the patient will be cured in 1 month or more but not more than 3 months \(=\frac { 165 }{ 400 } =\frac { 33 }{ 80 } \)
9.
Total number of cards in the box = 100
(a) Numbers less than 14 are 2,3,4,5,6,7,8,9,10,11,12,13
Their number = 12
Probability that the number on the card is a number less than 14
\(=\frac { 12 }{ 100 } =\frac { 3 }{ 25 } \)
(b) Perfect square numbers are 4,9,16,25,36,49,64,81,100
Their number = 9
Probability that the number on the card is a number which is a perfect square
\(=\frac { 9 }{ 100 } \)
(c) Prime numbers less than 20 are 2,3,5,7,11,13,17,19
Their number = 8
Probability that the number on the card is a prime number less than 20
\(=\frac { 8 }{ 100 } =\frac { 2 }{ 25 } \)
10.
In the bag,
number of red balls = 5
number of white balls = 8
number of green balls = 4
number of black balls = 7
Total number of balls in the bag = 5 + 8 + 4 + 7 = 24
(i) Number of black balls = 7
Probability that the ball drawn is black =\(\frac { 7 }{ 24 } \)
(ii) Number of balls that are not green = 5 + 8 + 7 = 20
Probability that the ball drawn is not green =\(\frac { 20 }{ 24 } \) =\(\frac { 5 }{ 6 } \)
11.
Total number of days = 250
(i) Number of days on which the weather forecasts were correct = 175
Probability that on a given day it was correct = \(\frac { 175 }{ 250 } =\frac { 7 }{ 10 } \)
(ii) Probability that it was not correct on a given day=\(1-\frac { 7 }{ 10 } =\frac { 3 }{ 10 } \)
12.
P(likes the detergent) = \(\frac { 375 }{ 500 } \)
= \(\frac { 3 }{ 4 } \)
(ii) P(does not like the detergent)
= 1-p(likes the detergent)
= \(1-\frac { 3 }{ 4 } =\frac { 1 }{ 4 } \)
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