Math Journal

Problem: The prime numbers between 2 and 20 have a sum of 75.  List these numbers and explain why they are called prime numbers.

Write the problem in your own words:

Find the prime numbers between 2 and 20 that when added together equal 75.  Write down the prime numbers between 2 and 20 and explain why they are prime numbers.

Solve:

3, 5, 7, 11, 13, 17, 19

Explain:

       After I read the question I realized that I did not understand or remember what a prime number is.  So the first thing I did was to look up the definition of a prime number in the dictionary.  I then found out that I didn’t know what the definition meant because I didn’t know the word unity.  After a discussion with my classmates I realized that unity means one.  Then I knew that a prime number is a number whose factors are one and itself. 

       The first number I tried was 17 because I knew that no other number besides 1 and 17 multiplied together equal 17.  I then began at two and checked all the multiples of the numbers between 2 and 9 to see if 17 was a multiple.  I stopped at 9 because 2 times 9 was 18 and that was greater than 17.  I then started at 3 and asked myself if there was any other multiple besides 3 and 1.  I did this all the way up to 19.  By the way I didn’t check the even numbers because I know they are all multiples of two.  The last thing I did was to check to see if I had all of the prime numbers.  I did this by adding up all of the prime numbers and seeing if it equaled 75.  It did and I was done!!