Slips of letters of the word ‘BACKGROUND’ are put in a bowl and thoroughly mixed. One slip is picked up at random. Find the probability that picked up slip’s letter is (i) a vowel (ii) present in the word ‘BALL’.
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Answer: (i) 103 (ii) 51
BACKGROUND has 10 letters: B, A, C, K, G, R, O, U, N, D.
(i) Vowels: A, O, U, i.e. 3. P = 3/10.
(ii) Letters also in 'BALL': B and A, i.e. 2 slips. P = 2/10 = 1/5.
A bag contains 25 balls. Some of them are yellow and others are green. One ball is drawn at random. If probability of getting a green ball is 3/5, then find the number of yellow balls.
A coin is dropped at random on the rectangular region shown in the figure. What is the probability that it will land inside the circle with radius 0.7 m ?
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Answer:30077 (about 0.257)
Area of rectangle =3×2=6 m2.
Area of circle =722×0.7×0.7=1.54 m2.
P(coin lands inside the circle) =61.54=600154=30077.
A bag contains 40 marbles out of which some are white and others are black. If the probability of drawing a black marble is 53, then find the number of white marbles.
In a pre-primary class, a teacher put cards numbered 20 to 59 in a bowl. A student picked up a card at random and read the number. Find the probability that the number read was (i) a prime number (ii) a perfect square.
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Answer: (i) 409 (ii) 403
Total cards =59−20+1=40.
(i) Primes: 23, 29, 31, 37, 41, 43, 47, 53, 59, i.e. 9 cards. P =409.
(ii) Perfect squares: 25, 36, 49, i.e. 3 cards. P =403.
A box contains 120 discs, which are numbered from 1 to 120. If one disc is drawn at random from the box, find the probability that (i) it bears a 2– digit number (ii) the number is a perfect square.
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Answer: (i) 43 (ii) 121
Total outcomes = 120.
(i) 2-digit numbers are 10 to 99, i.e. 90 numbers. P = 12090=43.
(ii) Perfect squares up to 120: 1, 4, 9, ..., 100, i.e. 10 numbers (112=121>120). P =12010=121.
The probability of guessing the correct answer of a certain test question is 12x. If the probability of not guessing the correct answer is 65, then find the value of x.
Two friends Anil and Ashraf were born in the December month in the year 2010. Find the probability that : (i) they share same date of birth. (ii) they have different dates of birth.
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Answer: (i) 311 (ii) 3130
December has 31 days. Whatever Anil's date is, Ashraf's date can be any of 31 equally likely days.
Saima and Aryaa were born in the month of June in the year 2012. Find the probability that : (i) they have different dates of birth. (ii) they have same date of birth.
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Answer: (i) 3029 (ii) 301
June has 30 days. Whatever Saima's date is, Aryaa's date can be any of 30 equally likely days.
Renu and Simran were born in the year 2000 which is a leap year. Find the probability that : (i) both have same birthday. (ii) both have different birthdays.
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Answer: (i) 3661 (ii) 366365
A leap year has 366 days. Whatever Renu's birthday is, Simran's can be any of 366 equally likely days.
While shuffling a pack of 52 cards, one card was accidently dropped. Find the probability that the dropped card (i) is not a face card. (ii) is a black king.
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Answer: (i) 1310 (ii) 261
Total outcomes = 52.
(i) Face cards = 12, so non-face cards = 40. P=5240=1310
All the face cards are removed from the pack of 52 cards and a card is drawn at random from the remaining cards. Find the probability that the card so drawn is (i) a spade. (ii) not an ace.
From a pack of 52 cards, all aces and all kings are removed. A card is drawn at random from the remaining cards. Find the probability that the card so drawn is (i) a face card. (ii) a card of red colour.
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Answer: (i) 112 (ii) 21
Remaining cards =52−8=44.
(i) Face cards left (jacks and queens) =8. P=448=112
The number of red balls in a bag is three more than the number of black balls. If the probability of drawing a red ball at random from the given bag is 2312, find the total number of balls in the given bag.
A bag contains cards which are numbered from 5 to 100 such that each card bears a different number. A card is drawn at random. Find the probability that number on the card is (i) a perfect square (ii) a 2-digit number
A bag contains balls numbered 2 to 91 such that each ball bears a different number. A ball is drawn at random from the bag. Find the probability that (i) it bears a 2– digit number (ii) it bears a multiple of 1.
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Answer: (i) 4541 (ii) 1
Total balls =91−2+1=90
(i) 2-digit numbers: 10 to 91, i.e. 82 balls. P=9082=4541
(ii) Every number is a multiple of 1, so all 90 balls qualify. P=9090=1
A bag contains 4 red, 5 white and some yellow balls. If probability of drawing a red ball at random is 51, then find the probability of drawing a yellow ball at random.
15 defective pens are accidentally mixed with 145 good ones. One pen is taken out at random from this lot. Determine the probability that the pen taken out is a good one.
A lot consists of 165 ball pens of which 30 are defective and the others are good. Rakshita will buy a pen if it is good. The shopkeeper draws one pen at random and gives it to Rakshita. What is the probability that she will buy it ?
There are 80 cards numbered from 1 to 80. One card is drawn at random from them. Find the probability that the number on the selected card is not divisible by 8.
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Answer:87
Numbers from 1 to 80 divisible by 8: 8, 16, ..., 80, i.e. 10 numbers.
In a pack of 52 playing cards one card is lost. From the remaining cards, a card is drawn at random. Find the probability that the drawn card is queen of heart, if the lost card is a black card.
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Answer:511
After a black card is lost, 51 cards remain.
The queen of hearts is red, so it is still in the pack: 1 favourable outcome.
One card is drawn at random from a well shuffled deck of 52 cards. Find the probability that the card drawn (i) is queen of hearts; (ii) is not a jack.
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Answer: (i) 521 (ii) 1312
Total outcomes = 52.
(i) There is 1 queen of hearts, so P = 521.
(ii) There are 4 jacks, so 48 cards are not jacks. P = 5248=1312.
A carton consists of 60 shirts of which 48 are good, 8 have major defects and 4 have minor defects. Nigam, a trader, will accept the shirts which are good but Anmol, another trader, will only reject the shirts which have major defects. One shirt is drawn at random from the carton. Find the probability that it is acceptable to Anmol.
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Answer:1513
Anmol accepts all shirts except those with major defects: 60−8=52 shirts.
The king, queen and ace of clubs and diamonds are removed from a deck of 52 playing cards and the remaining cards are shuffled. A card is randomly drawn from the remaining cards. Find the probability of getting (i) a card of clubs. (ii) a red coloured card.
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Answer: (i) 235 (ii) 21
Cards removed: 3 clubs and 3 diamonds, so 52−6=46 cards remain.
(i) Clubs left =13−3=10; P(club) =4610=235.
(ii) Red cards left =13 hearts +10 diamonds =23; P(red) =4623=21.
From a well-shuffled deck of 52 playing cards, all diamond cards are removed. Now, a card is drawn from the remaining pack at random. Find the probability that the selected card is a king.
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Answer:131
Cards left after removing 13 diamonds = 52 − 13 = 39
A box contains 20 discs which are numbered from 1 to 20. If one disc is drawn at random from the box, then find the probability that the number on the drawn disc is a (i) 2-digit number (ii) number less than 10
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Answer: (i) 2011 (ii) 209
Total outcomes = 20.
(i) 2-digit numbers: 10 to 20, i.e. 11 numbers. P =2011.
(ii) Numbers less than 10: 1 to 9, i.e. 9 numbers. P =209.
A bag contains 30 discs numbered from 1 to 30. One disc is drawn at random from the bag. Find the probability that it bears a number (a) divisible by 6. (b) greater than 25.
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Answer: (a) 61 (b) 61
Total outcomes = 30.
(a) Multiples of 6: 6, 12, 18, 24, 30, i.e. 5 numbers. P =305=61.
(b) Numbers greater than 25: 26, 27, 28, 29, 30, i.e. 5 numbers. P =305=61.
A bag contains 4 red, 3 blue and 2 yellow balls. One ball is drawn at random from the bag. Find the probability that drawn ball is (i) red (ii) yellow.