# Prime Numbers – Practice ProblemsHaving fun while studying, practice your skills by solving these exercises!

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A prime number is a number that is only divisible by one and itself. Prime numbers are used in cryptography or in creating algorithms that have important security applications. Prime numbers are also useful in generating Pseudo-Random numbers and in creating error correcting codes in computers. Other practical applications of prime numbers are seen in developing machine tools and in designing the metal racks of microwave ovens where utilizing primes help avoid the possibility of harmonics that could harm these machines. Learn how to determine whether a number is prime or not by helping Roscoe, the world’s foremost diamond hunter, identify the rocks which contain diamonds with the aid of his machine that test for prime numbers. Common Core Reference: CCSS.MATH.CONTENT.4.OA.B.4

Exercises in this Practice Problem
 Determine which numbers are prime. Use the sieve to find all the prime numbers. Decide if each number is prime or composite. Decide the possible side lengths. Explain what "being divisible by" means. Check the following statements.