Number Rules

Card Set Information

Author:
jmacnish
ID:
36555
Filename:
Number Rules
Updated:
2010-09-22 07:16:12
Tags:
Maths
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Description:
helps remember large division sums
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  1. What is the divisibility by 3 Rule
    • A number is divisible by 3 if the sum of its digits can be divided by 3.
    • Eg 12 1 + 2 = 3 And 3 is divisible by 3 so the number 12 is also divisible by 3.
  2. What is the divisibility by 4 Rule
    • A number is divisible by 4 if the number's last two digits are divisible by 4.
    • eg 112= since the last two digits, 12, are divisible by 4, the number 112 is
    • satisfies this rule and is also divisible by 4.
  3. How do you work out if a number is divisible by 6
    • if it is divisible by 2 AND 3.
    • eg 12 satisfies both conditions:
    • 1) 12 is even
    • 2) the sum of its digits (1+2 =3) is divisible by 3. Therefore, 12 passes this test.
  4. What is the divisibility by 8 Rule
    • A number passes the test for 8 if the last three digits form a number can be divided by 8.
    • eg 9,640 640 ÷ 8 = 80 so the whole number, 9,640, is divisible by 8
  5. What is the divisibility by 9 Rule
    • A number is divisible by 9 if the sum of the digits are evenly divisibly 9.
    • eg 4,518 4+5+1+8=18 and since 18 ÷9 = 2 , the whole number, 4,518, is divisible by 9
  6. What is the divisibility by 11 Rule
    • A number passes the test for 11 if the difference of the sums of alternating digits is divisible by 11.
    • 946 (9+6) - 4 = 11 which is, of course, evenly divided by 11 so 946 passes this divisibility test
    • 10,813 (1+8+3) - (0+1) = 12-1 =11. Yes, this satisfies the rule for 11!
    • 25, 784 = (2+ 7 + 4) - (5+8) = 13 - 13 =0 . Yes, this does indeed work. In case you found this last bit confusing, remember that any number evenly divides 0. Think about it, how many 11's are there in 0? None, right. Well that means
    • that 11 divides zero, zero times!

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