How are fifteen and flatter not alike

In comparing both words, it can be observed that they have similarities and differences. The similarities are that both words start with the letter ‘f’. Also both words have a letter that is repeated; ‘e’ for fifteen and ‘t’ for flatter. Both words have 2 kinds of vowels; ‘i’ and ‘e’ for fifteen and ‘a’ and ‘e’ for flatter. Both words also have 7 letters. The main difference between the two is the meaning. Another difference is the words end differently; ‘n’ for fifteen and ‘r’ for flatter.