• My age
• My house number
• The sum of those first two numbers
• The difference between those first two numbers
• Half of one of those first four numbers

I chose to write down the names of the numbers in letters rather than use digits (e.g. "thirty six").
Surprisingly, I noticed that each of the five numbers had the same number of letters in its name.

What were the last three numbers I wrote?

But if 98 is intended as the fifth number, (1) it has more than nine letters, (2) it's twice one of the first four rather than half.

If 49 is the intended fifth number, (1) it's the same as one of the other numbers, (2) it's not half of any of the first four, but rather half of 98, which isn't one of them.