As a curious learner, today I asked myself about the spelling of one number, because this, in particular, confuses me a lot. I typed twenty two in Google, and I observed that form but twenty-two was there as well. Why does it happen? Moreover, which one is the most grammatical?
Twenty two
Or
Twenty-two
Twenty-two
is the "correct" way. That was the way I was taught in school, and how dictionaries show it. However, people use "twenty two" occasionally, and though it is wrong, and grammar nazis will pick you out, unless you are writing in school or work, it won't really matter.
See Google Ngram for usage:
As you can tell, "twenty-two" is much more popular, and "twenty two" has fallen from obscurity to near burnination.
twenty twointo Google. For example, a search like this one would have been much more fruitful.