how long is a piece of string?'

One end t' other - precisely.

"Double the distance from one end to the middle" - also precisely is my usual response to that question. It's one of several routine sayings that cause my daughters to roll their eyes. Another occurs whenever a shop assistant asks me
"Are you right?"
and I respond, with a smile,
"When I was younger, the customer was always right."

Occasionally I'll add "Confused, irritating, hopeless and often mistaken, but always right."

Cheers, Rowan