The answer is 2 (without having to get lucky).

Explanation, please.

Oh, by Gud saying that I think I figured out how to do it in two. Start with three piles of three and weigh two of them. One will be lighter, or the one that is not weighed will be lighter. Repeat with the three pennies in the lighter stack.

Man, my body is really stressing over the layoffs even though my rational brain is not worrying about it. Between the dream and a flare up of my trigeminal neuralgia, my stress systems are in high gear. Which is totally at odds with my current mind set, which is fairly focused and not obsessing about when, who, if, why.

Or maybe it is just internalized stress over the baseball game (fell asleep before it was over) plus the election plus the work layoffs this week and at the end of the month plus generalized work stress. Oh there is also the lower back pain that I've been going to PT for and my last PT session created a bunch of pain in my right hip (could only do .5 of a mile on the treadmill yesterday before the pain was too much).

I guess there is a lot going on. But dang body...I can't control much and I'm doing what I can on the rest. The Cubs won, I've already voted, my kids have voted, and C is getting his Colorado Drivers License so he can vote, work layoffs will happen and if it is me, I should get at least 6 months worth of pay, general work stuff is what it is and I'm plugging away at what I can and finally I'm doing my PT exercises.

If I take a Lorazepam I'm afraid I'd fall asleep and I have work to do. I may crawl in bed once I'm done with work though. Only good spot at the moment - I have a few more days off of school, next class starts Monday.

Minimum means, you got lucky and found it fast, right?

In that case, you can do it with a minimum of ONE: Pick two pennies at random, and weigh them. If the two pennies don't weigh the same, then you got lucky and got it on the first pick.

Ahh -- my team member just asked me if she could be involved with next summer's internship program. Which would likely be a huge burden, but I'm so glad she asked before committing! That's all I need.

Start with three piles of three and weigh two of them. One will be lighter, or the one that is not weighed will be lighter. Repeat with the three pennies in the lighter stack.

Ahhhh, I knew there was a tricksy way I'd forgotten! This was in a book of math/logic puzzles I had as a kid, but I haven't revisited them in years.

Oh, by Gud saying that I think I figured out how to do it in two.

That's it.

Just got my new power bill. As I was hoping, the savings with an apartment-based power bill vs. a house bill with attendant sewer/taxes/etc very nearly balances the increase in basic rent. And the change in the gas bill where I'm only heating a one-bedroom, well-insulated apartment vs. a three-bedroom crappy house makes up the rest. (insert GIF of Hilary waggling her shoulders in glee)

Start with three piles of three and weigh two of them. One will be lighter, or the one that is not weighed will be lighter. Repeat with the three pennies in the lighter stack.

But that wouldn't narrow it to the single lighter penny, would it? Just to the stack with the lighter penny in it.

If the first two stacks you weigh are even you know that the lighter Penny is in the third stack. If they're not, you know which of the two stacks has the lighter penny. Then weigh two pennies from the lighter stack. If they're even, it's the third penny. If not, you'll know which one is lighter. So you only have to weigh twice, right?