“Okay,” mumbled Adam to himself, “if ‘a’ is the first set of assumptions and ‘b’ is the second set, then the probability of having it come from either ‘a’ or ‘b’ is . . . .”

“What’s he doing?” Joe asked, waving the apple he’d just picked up from the bowl on the table at his brother.Adam was hunched over their father’s desk writing on one of several pieces of paper that were strewn all over the top.Books were open to pages of what looked like chicken scratches to Joe, held in place by various items from an inkwell to another apple, and two pens were saved from rolling onto the floor only by the framed portrait of Elizabeth Cartwright.

Appropriate, thought Joe, as only Adam’s mother could possibly have understood what her son was up to.

Hoss shook his head and went back to the bridle he was repairing.“I dunno.He’s been sittin’ there for nigh on to three hours, workin’ his way through that new book he got.”

“. . . so the probability of picking one ball out of a hundred numbered balls that’s either odd or between eighty and one hundred . . .”

“Why?”

“It’s fun?” Hoss hazarded a guess.

Joe raised his eyebrows and glanced sideways towards the desk again.“Fun for him, maybe.Seems like a lot of work to me.” He wandered over, munching on his apple.

“. . . so P, the probability, of A intersecting with B is P of A (one half) plus P of B (one fifth), minus P of A (point five) times P of B (point two), which is point seven minus point one, equals—”

“Three in five,” inserted Joe.

“Huh?” asked Adam, his head coming up with a glazed expression on his face like he’d just been woken from a dream.

“Three in five chance,” Joe repeated.

He could see the calculations running through his brother’s mind.“You’re right.”He looked down at his numbers, up at Joe, and his eyebrows drew together in confusion.“How did you do that?You hate mathematics.”

“It’s easy.Half the numbered balls are odd, and another ten are between eighty and a hundred.That’s sixty balls out of a hundred, six in ten, three in five.Why d’you make it so hard?”He tossed his apple core in the ash can and sauntered outside.

Adam’s gaze followed Joe, then swung a bewildered look back to Hoss.“Because it’s fun?”