Divisibility and Mental Math

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Divisibility and Mental Math

• Lesson 3-1

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Vocabulary
A number is divisible by another number if it can
be divided into and result in a remainder of 0.
24 is divisible by 4, because 24 4 6. 24 is
not divisible by 5, because 24 5 4.8 (or 4R4).
An even number ends with a 0, 2, 4, 6, or 8.
An odd number ends with a 1, 3, 5, 7, or 9.
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Divisibility Rules
2 divides into all even numbers.
3 divides into a number if the sum of the digits
of that number is divisible by 3.
5 divides into numbers that end with a 5 or 0.
9 divides into a number if the sum of the digits
of that number is divisible by 9.
10 divides into numbers that end with 0.
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Example Test each number for divisibility by 3.
216
2 1 6 9
9 is divisible by 3, so 216 is divisible by 3.
yes
437
4 3 7 14
14 is not divisible by 3, so 437 is not divisible
by 3.
no
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Example Test the number for divisibility by 2,
5, or 10.
454,320
2 works because the number is even.
5 works because the number ends with 0.
10 works because the number ends with 0.
4 5 4 3 2 0 18.
Is the number divisible by 9?
18 is divisible by 9, so 454,320 is also
divisible by 9.
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Homework Time