REVISION TEST ( INTRODUCTION TO PROBABILITY )

11th Standard

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Maths

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Time : 01:30:00 Hrs
Total Marks : 100
    10 x 2 = 20
  1. If A and B are two independent events such that, P(A)=0.4 and P\((A\cup B)\)=0.9. Find P(B).

  2. A factory has two Machines-I and II. Machine-I produces 60% of items and Machine-II produces 40% of the items of the total output. Further 2% of the items produced by Machine-I are defective whereas 4% produced by Machine-II are defective. If an item is drawn at random what is the probability that it is defective?

  3. There are two identical urns containing respectively 6 black and 4 red balls, 2 black and 2 red balls. An urn is chosen at random and a ball is drawn from it.
    (i) find the probability that the ball is black
    (ii) if the ball is black, what is the probability that it is from the first urn?

  4. An experiment has the four possible mutually exclusive and exhaustive outcomes A, B, C, and D. Check whether the following assignments of probability are permissible.
    P(A) =\(\frac { 2 }{ 3 } \),  P(B)=\(\frac { 3 }{ 5 } \),  P(C)=-\(\frac { 1 }{ 5 } \),  P(D) =\(\frac { 1 }{ 5 } \)

  5. Five mangoes and 4 apples are in a box. If two fruits are chosen at random, find the probability that (i) one is a mango and the other is an apple (ii) both are of the same variety

  6. Eight coins are tossed once, find the probability of getting?
    (i) exactly two tails (ii) at least two tails (iii) at most two tails

  7. A bag contains 7 red and 4 black balls, 3 balls are drawn at random. Find the probability that (i) all are red (ii) one red and 2 black

  8. If P(\(\bar { A } \)) = 0.6 P(B) = 0.7 and \(P\left( \frac { B }{ A } \right) =0.4\) , then find \(P\left( \frac { A }{ B } \right) \)and \(P(A\cup B)\)

  9. The probability that student selected at random from a class will pass in Mathematics is \(\frac { 2 }{ 3 } \) and the probability that he passes in Mathematics and English is \(\frac { 1 }{ 3 } \). What is the probability that he will pass in English if it is known that he has passed in Mathematics?

  10. Events A and B are such that P(A) = \(\frac { 1 }{ 2 } \) , P(B) = \(\frac { 7 }{ 12 } \) and P(not A or not B) = \(\frac { 1 }{ 4 } \). State whether A and B are independent? 

  11. 6 x 3 = 18
  12. A problem in Mathematics is given to three students whose chances of solving A problem in Mathematics is given to three students whose chances of solving \(\frac { 1 }{ 3 } ,\frac { 1 }{ 4 } \) and \(\frac { 1 }{ 5 } \) (i) What is the probability that the problem is solved? (ii) What is the probability that exactly one of them will solve it?

  13. A firm manufactures PVC pipes in three plants viz, X, Y, and Z. The daily production volumes from the three firms X, Y and Z are respectively 2000 units, 3000 units, and 5000 units. It is known from the past experience that 3% of the output from plant X, 4% from plant Y and 2% from plant Z are defective. A pipe is selected at random from a day’s total production,
    (i) find the probability that the selected pipe is a defective one.
    (ii) if the selected pipe is a defective, then what is the probability that it was produced by plant Y?

  14. Three letters are written to three different persons and addresses on three envelopes are also written. Without looking at the addresses, what is the probability that
    (i) exactly one letter goes to the right envelopes
    (ii) none of the letters go into the right envelopes?

  15. The probability that a new railway bridge will get an award for its design is 0.48, the probability that it will get an award for the efficient use of materials is 0.36, and that it will get both awards is 0.2. What is the probability, that (i) it will get at least one of the two awards (ii) it will get only one of the awards.

  16. The probability that a girl, preparing for competitive examination will get a State Government service is 0.12, the probability that she will get a Central Government job is 0.25, and the probability that she will get both is 0.07. Find the probability that (i) she will get atleast one of the two jobs (ii) she will get only one of the two jobs.

  17. In a school there are 1000 students, out of which 430 are girls. It is known that out of 430, 10% of the girls study in class XII. What is the probability that a student chosen randomly studies in class XII given that the chosen student is a girl?

  18. 10 x 5 = 50
  19. Two thirds of students in a class are boys and rest girls. It is known that the probability of a girl getting a first grade is 0.85 and that of boys is 0.70. Find the probability that a student chosen at random will get first grade marks.
     

  20. Given P(A) = 0.4 and P(A\(\cup \)B)=0.7. Find P(B) if
    (i) A and B are mutually exclusive
    (ii) A and B are independent events
    (iii) P(A / B) = 0.4
    (iv) P(B / A) = 0.5

  21. A year is selected at random. What is the probability that
    (i) it contains 53 Sundays
    (ii) it is a leap year which contains 53 Sundays.

  22. Three coins are tossed simultaneously, what is the probability of getting
    i) exactly one head 
    ii) at least one head
    iii) at most one head?
     

  23. An advertising executive is studying television viewing habits of married men and women during prime time hours. Based on the past viewing records he has determined that during prime time wives are watching television 60% of the time. It has also been determined that when the wife is watching television, 40% of the time the husband is also watching. When the wife is not watching the television, 30% of the time the husband is watching the television. Find the probability that
    (i) the husband is watching the television during the prime time of television
    (ii) if the husband is watching the television, the wife is also watching the television

  24. An anti-aircraft gun can take a maximum of four shots at an enemy plane moving away from it. The probability of hitting the plane in the first, second, third, and fourth shot are respectively 0.2, 0.4, 0.2 and 0.1. Find the probability that the gun hits the plane.

  25. A main road in a City has 4 crossroads with traffic lights. Each traffic light opens or closes the traffic with the probability of 0.4 and 0.6 respectively. Determine the probability of
    (i) a car crossing the first crossroad without stopping
    (ii) a car crossing first two crossroads without stopping
    (iii) a car crossing all the crossroads, stopping at third cross.
    (iv) a car crossing all the crossroads, stopping at exactly one cross.

  26. A factory has two machines I and II. Machine I produces 40% of items of the output and Machine II produces 60% of the items. Further 4% of items produced by Machine I are defective and 5% produced by Machine II are defective. An item is drawn at random. If the drawn item is defective, find the probability that it was produced by Machine II.

  27. The chances of X, Y, and Z becoming managers of a certain company are 4: 2 : 3. The probabilities that bonus scheme will be introduced if X, Y and Z become managers are 0.3, 0.5 and 0.4 respectively. If the bonus scheme has been introduced, what is the probability that Z was appointed as the manager?

  28. A consulting firm rents car from three agencies such that 50% from agency L, 30% from agency M and 20% from agency N. If 90% of the cars from L, 70% of cars from M and 60% of the cars from N are in good conditions
    (i) what is the probability that the firm will get a car in good condition?
    (ii) if a car is in good condition, what is probability that it has come from agency N?

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