OK, I get that we need to learn the numerals as well as the words, but surely you should start with the numbers spelt as words so the learners get aquainted with their pronunciation before being taught to use the numerals. Also, it's going to be hell doing the listening exercises for this skill because a listening exercise can only have one answer and if you combine sentences with numerals and sentences with numbers spelt as words in the same lesson, there will be no way to figure out which is which.