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