Maths:7 Interesting facts

1. Letters 'a', 'b', 'c' &'d' do not appear anywhere in the spellings of 1 to 99
2. Letter 'd' comes for the first time in Hundred
3. Letters 'a', 'b' & 'c' do not appear anywhere in the spellings of 1 to 999
4. Letter 'a' comes for the first time in Thousand
5. Letters 'b' & 'c' do not appear anywhere in the spellings of 1 to 999,999,999
6. Letter 'b' comes for the first time in Billion
7. And Letter 'c' does not appear anywhere in the spellings of entire English counting