Dividing Tricks - 6. No short method has been found for...

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Several tests for divisibility are listed in the following paragraphs: 1. A number is divisible by 2 if its right-hand digit is even. 2. A number is divisible by 3 if the sum of its digits is divisible by 3. For example, the digits of the number 6,561 add to produce the sum 18. Since 18 is divisible by 3, we know that 6,561 is divisible by 3. 3. A number is divisible by 4 if the number formed by the two right-hand digits is divisible by 4. For example, the two right-hand digits of the number 3,524 form the number 24. Since 24 is divisible by 4, we know that 3,524 is divisible by 4. 4. A number is divisible by 5 if its right-hand digit is 0 or 5. 5. A number is divisible by 6 if it is even and the sum of its digits is divisible by 3. For example, the sum of the digits of 64,236 is 21, which is divisible by 3. Since 64,236 is also an even number, we know that it is divisible by 6.
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Unformatted text preview: 6. No short method has been found for determining whether a number is divisible by 7. 7. A number is divisible by 8 if the number formed by the three right-hand digits is divisible by 8. For example, the three right-hand digits of the number 54,272 form the number 272, which is divisible by 8. Therefore, we know that 54,272 is divisible by 8. 8. A number is divisible by 9 if the sum of its digits is divisible by 9. For example, the sum of the digits of 546,372 is 27, which is divisible by 9. Therefore we know that 546,372 is divisible by 9. Practice problems. Check each of the following numbers for divisibility by all of the digits except 7: 1. 242,431,231,320 2. 844,624,221,840 3. 988,446,662,640 4. 207,634,542,480 Answers: All of these numbers are divisible by 2, 3, 4, 5, 6, 8, and 9....
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