How long does it take to memorise your address?

How long have we lived in this house? Almost three and a half years. Forty-two months. Quite a long time. That's why it surprised me on Friday evening when there was a knock on the door and a delivery guy asked "This 250"? No, answered Steven, "This is 265.
He has had two of the numbers transposed since we first looked at this place, and he still can't get it right. His excuse when challenged about his lack of precision? "I'm not good with numbers".
He's a statistician.