David Hobby wrote: > >> 4 and 6 are simple, but not so much. The rule for 8 is, IMHO, horrible. > > Let's agree that the rule for 4 is usually easy for anyone > who knows their multiplication tables (out to 8x12, I guess). You > look at the last two digits, and see if they form a multiple of 8 > or are 4 more than a multiple of 8. > This is not the test I was thinking about. The test is: <even><multiple of 4> -or- [like 28, 84] <odd><even but not multiple of 4> [like 16, 92]
> Now for the rule for 8. It splits into two cases. If the > 100s digit is even, the last two digits must form a multiple of 8. > If the 100s digit is odd, the last two digits must form 4 more than > a multiple of 8. > Ok, but you have to agree that Simplicity is not within this test :-) >> I am imagining _small_ numbers, those that 5-th grade students >> are required to factor. > > But if the numbers are small, why not just divide? > Because dividing takes more time than doing the test. > Division is relatively painless if you don't have to keep > track of what the quotient is, but only care about the > remainder. > Tell that to a 10-year-old kid :-) Alberto Monteiro _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
