Question

Suppose you have 10 marbles, They are marked with the numbers: 1,2,3,4,5,6,7,8,9 or 10. They are placed in a jar and you reach in and select one. What is the probability that the number you select has a factor of 3?. What is the probability that the number you select is a prime number?. Even number?. Evenly divisible by 13?.

Answer 1

Factor of 3 = 3/10
Prime = 1/2
Even = 1/2
Evenly divisible by 13 = no chance

Answer 2

Total number of marbles = 10

Total number of marbles that has a factor of 3 = 3
They are {3, 6, 9)

P(factor of 3 ) = 3/10

Total number of marbles that is a prime number = 4
They are {2, 3, 5, 7}

P(Prime Number) = 4/10 = 2/5

Total number of marbles that is even: 5
They are {2, 4, 6, 8, 10}

P(even) = 5/10 = 1/2

Total number of marbles that is divisible by 13 = 0

P(divisible by 13) = 0/10 = 0