帮忙回答下面一道数学题How many whole number from 0 to 1,000 have digits
3个回答
sixty-three.
as a number with 3 digits,when the highest digit is 9,the second digit and the lowest digit only have ,10 minus 9 and then plus 1,
two changes 1-0;0-1
when the highest digit is 8,the second digit and the lowest digit have ,10 minus 8 and then plus 1,three changes 2-0;1-1;0-2
the rest may be deduced by analogy
when the highest digit is 1,the second digit and the lowest digit have ,10 minus 1 and then plus 1,10 changes 9-0;8-1;7-2;6-3;5-4;4-5;3-6;2-7;1-8;0-9
when the highest digit is 0,the second digit and the lowest digit have 9 changes,9-2;8-2;7-3;6-4;5-5;4-6;3-7;2-8;1-9
so,made the problems as below:
10+9+8+7+6+5+4+3+2+9=63
10 and 9 and 8 and 7 and 6 and 5 and 4 and 3 and 2 and 9 is 63
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