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Primes, Composites, and Divisibility

Primes, Composites, and Divisibility. What does divisible mean?. A number is divisible by another number if the quotient and divisor are whole numbers. 42 6 = 7 quotient divisor dividend. When is a number divisible by… 2? 3? 4?.

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Primes, Composites, and Divisibility

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  1. Primes, Composites, and Divisibility

  2. What does divisible mean? A number is divisible by another number if the quotient and divisor are whole numbers. 42 6 = 7 quotient divisor dividend

  3. When is a number divisible by… 2? 3? 4? A number is divisible by … 2 if the last digit is even (0, 2, 4, 6, 8) 3 if the sum of the digits is divisible by 3 (45 is divisible by 3 because 4 + 5 is divisible by 3) 4 if the last two digits are divisible by 4; also even (412: 12 is divisible by 4)

  4. When is a number divisible by… 5? 6? 9? A number is divisible by … 5 if the last digit is 0 or 5 (15, 70, 225) 6 if the number is divisible by both 2 and 3 9 if the sum of the digits is divisible by 9 (972: 9+7+2 is divisible by 9)

  5. Example 1:Tell whether 610 is divisible by 2, 3, 4, and 5. 610 • Yesthe last digit is even • No6+1+0=7 not divisible by 3 • No10 is not divisible by 4 • Yesthe last digit is 5

  6. Example 2:Tell whether 387 is divisible by 6, 9, and 10. 387 6 Nosince 387 is not even it is not divisible by 2 9 Yes3+8+7=18, which is divisible by 9 10 Noit does not end in a 0

  7. What is a composite number? A composite number is any number greater than 1 that has more than two factors

  8. What is a prime number? A prime number has only two factors: 1 and itself.

  9. Example 3:Tell whether each is prime or composite • 45 composite 1 x 45, 3 x 15, 5 x 9 (B) 13 prime 1 x 13 (C) 19 prime 1 x 19 (D) 49 composite 1 x 49, 7 x 7

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