Your guess is as good as mine
I do not know.
Mark’s eyes almost popped. It was four years since he had heard the sound, but he knew at once what it was. “Gosh! A dog! How do you s’pose he got here?”
“I don’t know,” said Sam. “Your guess is as good as mine.”
Dead Man’s Planet William Morrison
“Then what makes this planet so heavy?” Reba asked.
Junior shrugged helplessly and collapsed into a chair. “Your guess is as good as anybody’s.”
The Gravity Business James E. Gunn
“But what has happened to the by-product of the reaction?”
“Your guess is as good as mine. I have not had time to study that phase of it. Heat, mainly, was produced. Possibly a few atoms of helium. But the substance is gone. That is our chief concern just now.”
Spawn of the Comet Harold Thompson Rich
“Think it was Jacks?”
“One guess is as good as another. I’d like to hear what Del has to say about this. Maybe he’s down in the mine?”
Motor Matt’s Daring, or, True to His Friends Stanley R. Matthews