標題:
1,2,3,4,5,7,8,10,11,13,17,19,39的整除性的檢定
發問:
1,2,3,4,5,7,8,10,11,13,17,19,39的整除性的檢定10points 更新: 答其中三個數都okay
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最佳解答:
(I) Divided by 2 --- Any EVEN number --- e.g. 22, 46 (II) Divided by 3 --- Add up the digits of the number. If the sum is divisible by 3, the number is divisible by 3 --- e.g. 372: 3+7+2=12 which is divisible by 3. Then 372 is divisible by 3 --- e.g. 724: 7+2+4=13 which is NOT divisible by 3. Then 724 is NOT divisible by 3 (III) Divided by 5 --- Any number end with 5 or 0 --- e.g. 45, 90, 123467865 (IV) Divided by 4 --- Any number with LAST 2 DIGIT divisible by 4 --- e.g. 468: since 68 is divisible by 4, 468 is divisible by 4 --- e.g. 1274: since 74 is NOT divisible by 4, 1274 is NOT divisible by 4 --- e.g. 12345678944: since 44 is divisible by 4, 12345678944 is divisible by 4 (V) Divided by 8 --- Any number with LAST 3 DIGIT divisible by 8 --- e.g. 1272: since 272 is divisible by 8, 1272 is divisible by 8 --- e.g. 12345678944: since 944 is divisible by 8, 12345678944 is divisible by 8 (VI) Divided by 11 --- (Step 1) 拿走該數的最後一個數字 --- (Step 2) 將剩下的數減去該數字 --- (Step 3) Repeat these 2 steps until you know the answer is divisible by 11 or not --- e.g. 6195354 619535 – 4 = 619531 61953 – 1 = 61952 6195 – 2 = 6193 619 – 3 = 616 61 – 6 = 55, which is divisible by 11 so 6195354 is divisible by 11!!! (VII) Divided by 7 --- (Step 1) 拿走該數的最後一個數字, 並將該數乘2 (let the answer be y) --- (Step 2) 將剩下的數減去y --- (Step 3) Repeat these 2 steps until you know the answer is divisible by 7 or not --- e.g. 366527 36652 – 7 x 2 = 36638 3663 – 8 x 2 = 3647 364 – 7 x 2 = 350 35 – 0 x 2 = 35, which is divisible by 7 so 366527 is divisible by 7!!! --- e.g. 12345 1234 – 5 x 2 = 1224 122 – 4 x 2 = 114 11 – 4 x 2 = 3, which is NOT divisible by 7 so 12345 is NOT divisible by 7 (VIII) Divided by 13 --- (Step 1) 拿走該數的最後一個數字, 並將該數乘4 (let the answer be y) --- (Step 2) 將剩下的數加上y --- (Step 3) Repeat these 2 steps until you know the answer is divisible by 13 or not --- e.g. 731042 73104 + 2 x 4 = 73112 7311 + 2 x 4 = 7319 731 + 9 x 4 = 767 76 + 7 x 4 = 104 10 + 4 x 4 = 26, which is divisible by 13 so 731042 is divisible by 13 (IX) Divided by 17 --- (Step 1) 拿走該數的最後一個數字, 並將該數乘5 (let the answer be y) --- (Step 2) 將剩下的數減去y --- (Step 3) Repeat these 2 steps until you know the answer is divisible by 17 or not --- e.g. 114852 11485 – 2 x 5 = 11475 1147 – 5 x 5 = 1122 112 – 2 x 5 = 102 10 – 2 x 5 = 0, which is divisible by 17 so 114852 is divisible by 17 (X) Divided by 19 --- (Step 1) 拿走該數的最後一個數字, 並將該數乘2 (let the answer be y) --- (Step 2) 將剩下的數加上y --- (Step 3) Repeat these 2 steps until you know the answer is divisible by 19 or not --- e.g. 99485 9948 + 5 x 2 = 9958 995 + 8 x 2 = 1011 101 + 1 x 2 = 103 10 + 3 x 2 = 16, which is NOT divisible by 19 so 99485 is NOT divisible by 19 (XI) Divisible by 39 --- When the number is divisible by BOTH 3 and 13 (since 3 x 13 = 39) -------------------------- Actually there is a RULE on that! Please refer to the below website: THE MATH FORUM ^_^
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