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kdog3683
United States916 Posts
729 = + Show Spoiler + 3^6 2048 = + Show Spoiler + 2^11 How would you do this quickly? 15seconds, no calculator. What is the process you go through? I divide by small #s, 2,3,4,5... If 2 fits, i divide by 2 again, else I try 3. Else, 4, etc, but this is slow.   | ||
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Durak
Canada3685 Posts
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Abydos1
United States832 Posts
On February 02 2009 11:16 kdog3683 wrote: Simplify to the form a^b LOL, thats not simplifying it. | ||
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naonao
United States847 Posts
but otherwise i do a branch thingy like for instance 144 would be like 144 / \ 12 12 / \ / \ 3 4 3 4 | / \ | / \ 3 2 2 3 2 2 Also some tips to know when numbers are divisible by others: 2: number is even 3: sum of the digits is a multiple of 3 4: last two digits are divisible by 4 5: ends in 0 or 5 6: even and the digits add up to a multiple of 3 7: NOTHING 8: last 3 digits are divisible by 8 9: sum of the digits is a multiple of 9 | ||
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paper
13197 Posts
but i think there are some tricks for some numbers | ||
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Malongo
Chile3479 Posts
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foppa
Canada451 Posts
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micronesia
United States24799 Posts
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Plexa
Aotearoa39261 Posts
 although there is a method to test if a number is dividable by 7.. its just so complicated that its quicker to just brute force it haha | ||
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Pwert
United States59 Posts
On February 02 2009 11:26 naonao wrote: Thats memorization. powers of 2 and powers of 3. but otherwise i do a branch thingy like for instance 144 would be like 144 / \ 12 12 / \ / \ 3 4 3 4 | / \ | / \ 3 2 2 3 2 2 Also some tips to know when numbers are divisible by others: 2: number is even 3: sum of the digits is a multiple of 3 4: last two digits are divisible by 4 5: ends in 0 or 5 6: even and the digits add up to a multiple of 3 7: NOTHING 8: last 3 digits are divisible by 8 9: sum of the digits is a multiple of 9 Actually, I know of this interesting (but time consuming) way of finding out if a number is divisible by 7. You take the digit farthest to the right, double it, and subtract it from the original number over and over until you have a number from 9 to negative 9. If it turns out to be 7, 0, or negative 7 then the number is divisible by 7. Example: 182 becomes (18 - 2) which equals 14. 14 becomes (1 - 8) which equals negative 7. 182 is divisible by 7. Example: 6881 becomes (688 - 2) which equals 686. 686 becomes (68 - 12) which equals 56. 56 becomes (5 - 12) which equals negative 7. 6881 is divisible by 7 Example: 531 becomes (53 - 2) which equals 51. 51 becomes (5 - 2) which equals 3. 531 is not divisible by 7. | ||
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