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Question
Cards marked with numbers 1, 2, 3, 4… 20 are well shuffled and a card is drawn at random. What is the probability that the number on the card is:
(1) A prime number,
(2) A number divisible by 3,
(3) A perfect square?
Solution
Total numbers = 20
1) the prime numbers are 2, 3, 5, 7, 11, 13, 17, 19 respectively
Favourable cases = 8
The probability of getting a prime number = `8/20 = 2/5`
2) the numbers divisible by 3 are 3 ,6 ,9 ,12 ,15 ,18 respectively
Favourable cases =6
Probability of getting a number divisible by 3= `6/20 = 3/10`
3) the perfect squares are 1, 4, 9, 16 respectively
Favourable cases = 4
Probability of getting a perfect square number - `4/20 = 1/5`
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