Math Practice 101
Homework Explained - Math Practice 101

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Grade 4 HMH Go Math - Answer Keys


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The Sieve of Eratosthenes

Eratosthenes was a Greek mathematician who lived more than 2,200 years ago. He invented a method of finding prime numbers, which is now called the Sieve of Eratosthenes.

  • Question 19 (request help)

    Follow the steps below to circle all prime numbers less than 100. Then list the prime numbers.

    STEP 1
    Cross out 1, since 1 is not prime.

    STEP 2
    Circle 2, since it is prime. Cross out all other multiples of 2.

    STEP 3
    Circle the next number that is not crossed out. This number is prime. Cross out all the multiples of this number.

    STEP 4
    Repeat Step 3 until every number is either circled or crossed out.

    So, the prime numbers less than 100 are
  • Type below:
  • Question 20 (request help)

    Explain why the multiples of any number other than 1 are not prime numbers.
  • Type below:

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