Mason and I have been loosely following the coverage of the California wildfires. No vested interested, really; he just seemed curious about it and it seemed like a good opportunity to talk about “parenty-stuff” like “this is why we don’t play with matches” and stuff like that.

During Friday’s broadcast, it was reported that the fire was “36% contained.” Mason asked me how they knew the exact percentage and I had no answer for him. I mean, really? 36%? Then UPI reported 42%, and yesterday, CNN reported that they were now 49% contained.

Human beings are funny when it comes to numbers. For example, we tend to round numbers off to make them easier to deal with. Weathermen rarely predict a 33.45% chance of rain; they say 35% because it’s close enough and it gets the point across. On the flip side, when we hear even numbers, we tend to assume they’ve been rounded off. If someone tells you they paid $20k for a new car, very few of us would assume they paid $20,000.00 exactly. When we tell our friends we woke up at 6am, we don’t necessarily mean we awoke at 6am on the dot.

We do this so often that when we hear even numbers, we often assume they’ve been rounded off. Odd numbers, perhaps even on a subliminal level, make us assume that a number has not been rounded off. Telling someone that you got up at 6:04am implies that you woke at exactly 6:04am.

News reporters are in the business of presenting the truth. If we don’t believe reporters, they’ll be out of a job. Journalists have an inherent need to maintain our trust, and I suspect, that’s the reason for the numbers they’ve been reporting. You or I would probably say 35% vs. 36% and 50% vs. 49%, but where 50% sounds rounded and approximate, 49% implies a very specific measurement. 50% implies somebody looked at a map and said, “eh, it’s about half out.” 49% creates a vision of scientists and computer operators huddled together working with up-to-date maps, satellites and technical wizardry.

This was one of my favorite “mind reading” magic tricks as a kid:

“Pick a number between 1 and 50. Both digits in the number should be odd, like “13”, and the two digits should not be the same. Pick, quickly! Now, what was your number?”

Click below to view the results of the trick.

After the person told me their number I would produce a piece of paper with the number seventeen written on it, scratched out, and then the number 37 written next to it.

Like most magic tricks, this one involves psychology and misdirection. By telling someone to pick a number between 1 and 50, subconsciously you assume that you have fifty choices. Right off the bat, I’ve limited your choices with a couple of quick stipulations. The first is that both numbers must be odd. Your gut instinct is that I’ve limited you to 25 choices, but if you look, there are only 10: 11, 13, 15, 17, 19, 31, 33, 35, 37, 39. By adding the stipulation that both numbers can’t be the same, I’ve also eliminated 11 and 33, and most people won’t pick 13 after it’s mentioned, which leaves people with 7 choices. Most people seem to gravitate toward “7” because it doesn’t seem very round. That leaves you with 17 and 37. By writing both numbers down you really get two guesses. I never had anyone who picked “17” not appear impressed, even though it was marked out. “Shoulda stuck with my first guess,” I’d say.

I’m sure all of you are much to smart to fall into such a trap. For those of you who picked a different number, try this on five people tomorrow and see what numbers you get. I used to have a separate math trick waiting for people who picked something other than 17 or 37 that went like this:

“Now take your number, spell it out and count the number of letters. Now, do the same thing again, spelling out the new number and counting the number of letters. Continue this until you get the same number twice in a row.”

Once they reached “four” I would pull out another piece of paper with the number “4” written on it, surrounded by some magic symbols I found out of an old book I had stolen (er, “made disappear!”) from the library. It’s not as good as the first trick, but it was a nice backup to have on hand in case the first one didn’t work.