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E x a m p l e . Find LCM for numbers: 168, 180 and 3024.
S o l u t i o n . 168 = 2 · 2 · 2 · 3 · 7 = 23 · 31 · 71 ,
180 = 2 · 2 · 3 · 3 · 5 = 22 · 32 · 51 ,
3024 = 2 · 2 · 2 · 2 · 3 · 3 · 3 · 7 = 24 · 33 · 71 .
Write out the greatest powers of all prime factors: 24, 33, 51, 71
and multiply them:
LCM = 24 · 33 · 5 · 7 = 15120 . Divisibility criteria
Divisibility by 2. A number is divisible by 2, if its last digit is 0 or is divisible by 2. Numbers, which are
divisible by 2 are called even numbers. Otherwise, numbers are called odd numbers.
Divisibility by 4. A number is divisible by 4, if its two last digits are zeros or they make a twodigit number,
which is divisible by 4.
Divisibility by 8. A number is divisible by 8, if its three last digits are zeros or they make a threedigit number,
which is divisible by 8.
Divisibility by 3 and by 9 . A number is divisible by 3, if a sum of its digits is divisible by 3. A number is
divisible by 9, if a sum of its digits is divisible by 9.
Divisibility by 6. A number is divisible by 6, if it is divisible by 2 and by 3.
Divisibility by 5. A number is divisible by 5, if its last digit is 0 or 5.
Divisibility by 25. A number is divisible by 25, if its two last digits are zeros or they make a number, which is
divisible by 25.
Divisibility by 10. A number is divisible by 10, if its last digit is 0. Math I 6 Feel free to pass this on to your friends...
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 Spring '13
 OTIS

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