TMI: The Half-Life of Oranges

Recently, I've developed a habit of walking to a nearby grocery store every Sunday afternoon and buying three oranges and a bunch of bananas [along with some junk food to keep my diet "balanced"].

My intention is to eat an orange on Monday, Wednesday, and Saturday nights. Monday night all 3 oranges seem equally firm, so I pick one at random, and it tastes great. But by Wednesday night, one of the oranges has turned moldy and squishy and I'm forced to toss it out and eat the surviving orange which tastes just fine.

Now I could go to the store on Saturday night and make up for the lost orange (and I probably should burn the extra calories), but then I'd feel obligated to buy more stuff rather than stand in line with a single orange. So I have two of the bananas instead. Fortunately, the bananas seem to ripen much more predictably.

Guess I need some education on choosing oranges, or this Sunday, I'll buy 4 just to see what happens...