Question 105735: Which of the given numbers are composite?
0, 1, 15, 19, 23, 31, 49, 55, 59, 87, 91, 97, 103, 105
Help me with this problem please.
Answer by Fombitz(32388)   (Show Source):
You can put this solution on YOUR website! A composite number is a positive integer which has a positive divisor other than one or itself.
By definition, every integer greater than one is either a prime number or a composite number.
A couple of rules for hunting primes and composites.
If the number ends in an even digit, it is divisible by 2. (Example:314=2x157)
Add up the digits in a number and the sum is divisible by 3, the number is divisible by 3.
(Example:501, 5+0+1=6 which is divisible by 3, then 501 is divisible by 3, 501=3x167)
Ends in a 5 or 0, divisible by 5.(Example:665=5x133).
0 - neither prime nor composite
1 - neither prime nor composite.
15 - 3x5, composite (1+5=6, ends in 5)
19 - prime
23 - prime
31 - prime
49 - 7x7, composite
55 - 5x11, composite (ends in 5)
59 - prime
87 - 3x29, composite (8+7=15)
91 - prime
97 - prime
103 - prime
105 - 3x5x7, composite (1+0+5=6, ends in 5)
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