Exercise 15.1 25 Questions
Q1: A die is thrown once. Find probability of getting: (i) a prime number â†' {2,3,5} â†' 3/6=½. (ii) number between 2 and 6 â†' {3,4,5} â†' ½. (iii) an odd number â†' ½.
Q2: One card from well-shuffled deck of 52 cards. (i) a king of red colour â†' 2/52=1/26. (ii) a face card â†' 12/52=3/13. (iii) a red face card â†' 6/52=3/26. (iv) jack of hearts â†' 1/52. (v) a spade â†' 13/52=1/4. (vi) queen of diamonds â†' 1/52.
Q3: A piggy bank contains 50p, ₹1, ₹2, ₹5 coins in numbers 100:50:20:10. Falls out. Probability it is 50p â†' 100/180=5/9. ₹5 coin â†' 10/180=1/18.
Q7: Two coins tossed simultaneously. P(exactly 1 head) â†' {HT,TH}/4=½. P(at most 2 heads) â†' 1 (sure event).
Q10: A carton of 15 mobile phones contains 3 defective. A phone is drawn at random. P(it is NOT defective) â†' 12/15=4/5.
Q11: A box has 5 red, 8 white, 4 green marbles. P(red)=5/17, P(white)=8/17, P(green)=4/17, P(not green)=13/17.
Q13: Two dice thrown simultaneously. Total outcomes = 36. (i) sum is 6 â†' {(1,5),(2,4),(3,3),(4,2),(5,1)} = 5/36. (ii) a doublet â†' {(1,1),(2,2)...(6,6)} = 6/36=1/6.
Q15: Two dice, find probability: (i) sum is 10 â†' {(4,6),(5,5),(6,4)} = 3/36=1/12. (ii) product is 12 â†' more complex, count outcomes.
Q17: A lot of 20 bulbs contains 4 defective. One bulb drawn at random. P(defective)=4/20=1/5. P(not defective)=4/5.
Q19: P that a student of class was born in August = 1/12. Not born in August = 11/12.
Q20: A box of 90 discs numbered 1 to 90. P(two-digit) = 81/90=9/10. P(perfect square)=9/90=1/10. P(divisible by 5)=18/90=1/5.
Q22: A die is thrown once. P(number>6)=0, P(number≤6)=1. P(prime)
Q24: A die is thrown twice. Probability that (i) 5 will not come up either time â†' (5/6)²=25/36. (ii) 5 will come up at least once â†' 1âˆ'25/36=11/36.
Q25: Which argument is correct? Two dice: P(sum 10)=3/36=1/12. Argument about sum 11=2/36=1/18. Compare probabilities correctly.
Exercise 15.2 (Optional) 5 Questions
Two customers Shyam and Ekta visit a shop in same week (Tue to Sat). Each equally likely on any day. Find probability both visit on: (i) same day â†' 5×(1/5)(1/5)=1/5. (ii) consecutive days â†' 8/25. (iii) different days â†' 4/5.
Q2: A die numbered 1-6 on faces (two faces each of 1,2,3). P(1)=2/6=1/3, P(2)=1/3, P(3)=1/3.
Q4: A box of 12 balls: x black. If one ball drawn P(black)=x/12. If 6 more black added, P(black doubles). Find x. â†' (x+6)/18=2x/12 â‡' Solve: x=3.
Q5: A jar 24 marbles, some green, rest blue. P(green)=2/3. #green = (2/3)×24 = 16. Blue = 8.
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