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    Fractions and composite numbers problems.

    The question is: Sam wrote a two digit number. The number is a composite number and the number is also odd. Can someone explain to me how that could be possible? My son answered with the number of 89 and was wrong. Other number choices are: 23, 56, and 33. Thank you in advance.
  • #660895
    A composite number is defined as a positive integer which can be obtained by multiplying two smaller numbers other than 1. Always ignore 1 in these calculations. Even number is divisible by 2 while odd is not.

    For example 4 is a composite number because 2 x 2 = 4. It is also an even number.
    5 is a prime number. It is an odd number.
    Similarly 6 is a composite number because 2 x 3 = 6. It is an even number.
    7 is a prime number. It is an odd number.
    Also, 8 is a composite number because 2 x 4 = 8. It is an even number.
    9 is also a composite as 3 x 3 = 9. It is an odd number.
    and so on ...

    Based on above explanation -
    23 is a prime number not divisible by any smaller number (ignoring 1). It is an odd number.
    33 is a composite number because 3 x 11 = 33. It is an odd number.
    56 is a composite number because 7 x 8 = 56. It is an even number.
    89 is a prime number. It is an odd number.

    Just for information the list of composite numbers from 1 to 100 is -
    4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99 and 100.

    Knowledge is power.

  • #660897

    89 and 33 are the odd numbers from the choices you gave. Composite numbers are numbers that can be divided by a number other than itself. We can't divide 89 by anything other than 89. 33 on other hand can be divide by 3 and 11. So that is the correct answer.
    It is a fairly easy question.


    The stronger a light shines the darker are the shadows around it.

  • #660898
    Oh I just noticed that 23 is an odd number too but it's a prime so it's irrelevant. The answer is 33.
    The stronger a light shines the darker are the shadows around it.

  • #660922
    23, 56, and 33 are the numbers you have mentioned. Odd numbers can also be composite numbers. A composite number is a number which can be obtained by multiplying 2 numbers other than 1 and the number itself.
    21 is an odd number and it is a prime number also. 3 X 7 = 21.
    33 is an odd number and it is a prime number also 3X11 = 33.
    Like that there are some odd composite numbers also.

    drrao
    always confident

  • #686322
    First, we should know Three basic things.

    (I) A composite number is a positive integer which is not a prime number. Example - 4, 6, 8, 9, 10, 12, 14, 15, 16 and so on.

    (II) A prime number is a whole number greater than 1 whose only factors are 1 and itself. Example- 2, 3, 5, 7, 11, 13, 17, 19, 23 and so on.

    (III) When two odd numbers are multiplied together, the result is always an odd number.

    Now we are ready to find numbers which are Composit as well as odd numbers.

    The first condition is it should not be a prime number so it is clear Number should not be multiple of any Even number.

    Now we have to select a pair of odd numbers which are not prime numbers. 3,5,7,11,17,19 and so on .

    If we choose any pair of different numbers and multiply them it will satisfy both conditions i.e
    (I) The resulted product will not be a prime number because it will have 3 factors 1 and 2 different numbers we have chosen. , and
    (II) The resulted product shall be always an odd number because the product of two odd numbers is always an odd number.

    Now we can start finding numbers which are Composite as well as Odd.
    3 X 5 =15,
    3 X 7 = 21,
    3 X 11 = 33, and so on.

    You gave three options. 23, 56, and 33
    33 is the correct answer.

    Explanation
    33 is not a prime number because it has three factors 1,3 and 11.
    33 is an odd number.


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