how many natural numbers whose ten digits are smaller than the on_英语解答

how many natural numbers whose ten digits are smaller than the ones digits are there from 10 to 99?翻译这句话.

人气：105 ℃　时间：2020-06-01 07:25:05

解答

从10到99的自然数里,有多少个数,其中十位数比它的个位数小?
这里的ten digits 是十位数,
ones digits 是个位数