# If a number is chosen at random from the following list, what is the probability that it is not prime? 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

justaguide | College Teacher | (Level 2) Distinguished Educator

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We have a list of 10 numbers from 1 to 10 consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Now the prime numbers in this list are 2, 3, 5 and 7. We have to remember that 1 is not a prime number as a prime number is a number that has exactly 2 factors. So the numbers that are not prime are 1, 4, 6, 8, 9 and 10. There are 6 such numbers.

If a number is picked at random from this list the possibility of picking a number that is not prime is 6/10 or 3/5 or 60%.

The required probability is 60%.

neela | High School Teacher | (Level 3) Valedictorian

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The number of numbers in the list are 10.

The primes are 2, 3,5,7.

So the number of numbers which are prime in the list = 4.

Therefore , probability of an event = number of  ways of happening favourable to the eevent/ Total number of ways = 4/10 = 0.4.

Therefore  the prabability that if a number is chosen at random from the list of numbers: 1,  2,  3,  4 ,   5,   6,  7,   8,   9 and 10, the chose number is prime is 0.4.