Prime and Composite Numbers in Math - Grade 7 Math Questions With Detailed Solutions

What are prime and composite numbers in math? Grade 7 math questions are presented along with detailed solutions. Detailed Solutions and explanations are included.

What are prime and composite numbers in math?

A prime number is a whole number greater than 1 that can only be evenly divided by 1 and itself.

Examples: 2, 3, 5, 7, 11,... are prime numbers. If you try to divide them by numbers other than 1 or themselves, the remainder will not be zero.

A composite number is a whole number greater than 1 that can be evenly divided by 1, itself and other numbers.

Examples: 4, 6, 8,12..are composite numbers because:

42 = 2 , 4 is divisible by 1, itself and 2

62 = 3 , 63 = 2 , 6 is divisible by 1, itself, 2 and 3.

82 = 4 , 84 = 2 , 8 is divisible by 1, itself, 2 and 4.

122 = 6 , 123 = 4 , 124 = 3 , 126 = 2 , 12 is divisible by 1, itself, 2, 3, 4 and 6.

Answer the following Questions on Prime and Composite Numbers.

  1. Which of the following numbers are prime?
    1, 6.3, 11, 14, 13, 21, 23, 4/5, 100, 123 .

  2. Which of the following numbers are composite?
    1, 8.4, 15, 13, 9/2, 24, 33.

  3. List all prime numbers between 30 and 50 inclusive.

  4. List all composite numbers between 100 and 110 inclusive.

  5. Is the sum of two prime numbers always a prime number?

  6. Is the product of two prime numbers also a prime number?

  7. Which is the largest 3 digit prime number?

  8. Which is the smallest 2 digit prime number?

  9. List all the two digit prime numbers that can be made from the digits 1, 3 and 6 (used only once each).

  10. Can you find a prime number whose least significant digit (digit on the right) is 0?

  11. Can you find a prime number whose least significant digit (digit on the right) is 5?

  12. Can you find a prime number such that the sum of all its digits is equal to 12?

  13. Detailed Solutions and explanations are included.

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Updated: 20 January 2017 (A Dendane)