Jonathan's full name contains 8 letters for the first name and 10 letters for the surname. His sister's name has 5 letters for the first name and 10 letters for the second name. What's the total number of letters in their names? Let's answer step by step:
Jonathan has 8 + 10 = 18 letters in his name. His sister has 5 + 10 = 15 letters in her name. The total number of letters in their names is 18 + 15 = 33. The answer: 33.