Math Is Fun Forum

Joseph

Guest

6th grade math

A fair number crbe (numbered 1-6) is rolled twice. What is the probability that the first roll is a prime number, and the second roll is a composite number?

LuisRodg

Real Member

Registered: 2007-10-23

Posts: 322

Re: 6th grade math

First of all you need to know what numbers are the prime numbers. For numbers 1-6, the prime numbers are 2,3 and 5. So you have 3 prime numbers with a total outcome of 6 so the probability that the first roll is a prime number is 1/2

Rolling a die is an independent event, which means that rolling the second time doesnt depend on the first roll etc. For numbers 1-6, only 4 and 6 are composite numbers which means that you have a probability of getting a composite number of 2/6 or 1/3.

If you were asking for the probability of first getting a prime number AND THEN getting a composite number on the second roll then just multiply both events together: 1/2 * 1/3 = 1/6

So theres a 1/6 probability of getting a prime number on the first roll and then a composite number on the second roll.