第5个回答 2010-05-16
解:从这10个数码中任取3个,组成一3位数,使数字成等差数列,可按公差的大小分类讨论。即穷举法。(1)公差为1时,123,234,345,456,567,678,789,计7个。(2)公差为-1时,987,876,765,654,543,432,321,210。计8个。(3)公差为2时,135,246,357,468,579,计5个。(4)公差为-2时,975,864,753,642,531,420,计6个。(5)公差为3时,147,258,369,计3个。(6)公差为-3时,963,852,741,630,计4个。(7)公差为4时,159。计1个,(8)公差为-4时,951,840,计2个。综上知,有7+8+5+6+3+4+1+2=36个。