2007-07-25 22:25:39 · 2 answers · asked by Anonymous in Education & Reference ➔ Trivia
Most people can multiply by two easily. And base ten math makes multiplying or dividing by ten easy. But many people get stumped or freeze when they need to multiply by nine.
"Magic nines" make multiplication of 9s easy!
The integers of multiples of nine always add up to nine!
0 + 9 = 9 (1 x 9 = 9)
1 + 8 = 9 ( 2 x 9 = 18)
2 + 7 = 9 ( 3 x 9 = 27 )
3 + 6 = 9 ( 4 x 9 = 36 )
4 + 5 = 9 ( 5 x 9 = 45 )
54
63
72
81
90
Get it? The numbers in the left column always go up by one.
Numbers in the right column always go down by one.
Add those two Numbers together, they always equal nine!
That makes checking your work (when multiplying nines) very easy and sure!
2007-07-25 22:52:46 · answer #1 · answered by Aleph Null 5 · 1⤊ 0⤋
You can take any number evenly divisible by three and the sum of its digits is also evenly divisible by three.
Examples:
111 --- 1 + 1 + 1 = 3
1002 --- 1 + 0 + 0 +2 = 3
6987 --- 6 + 9 + 8 + 7 = 30
537 --- 5 + 3 + 7 = 15
2007-07-26 14:09:07 · answer #2 · answered by Menehune 7 · 0⤊ 0⤋