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10 cards are numbered from 1 to 10 and placed in a box. One card is selected at random and is not replaced. Another card is then randomly selected. What is the probability of selecting two prime numbers?
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There are 9*10=90 possible combinations. There are 3*4=12 possible prime number combinations: (2,3), (2,5), (2,7), (3,2), (3,5), (3,7), (5,2), (5,3), (5,7), (7,2), (7,3), (7,5). The probability is 12/90=2/15.
Last edited by Relentless (2019-10-17 23:46:17)
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Prime number 2,3,5,7 --- 4 primes
favourable pairs= c(4,2)=6, total pair=C(10,2)=45
Probability =6/45 =2/15
mycalsuite
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I like to calculate it this way:
Draw 1 has probability = 4/10.
If Draw 1 is a prime, then Draw 2 has probability = 3/9.
Product of these = 2/15.
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