"Tim Math"

I've never been particularly good at math. I remember distinctly in 4th grade our teacher would deduct points if she saw you using your fingers when you were adding or subtracting (or if she saw you counting things in the room, or any of the other tricks that are out there for essentially counting on your fingers but without the fingers.) The girl who sat next to me used to raise her hand and point at me if she thought I was doing it so that my teacher would come over and harass me about it. The problem is, while I agree that it's good to get away from using a counting mechanism, no one really ever taught me how to do math in my head - and to this day I still will fall back on my fingers or some other mechanism to double-check myself if there's not a calculator handy.

(Some of you may be scratching your head and thinking, "But I thought you said you were a software engineer?" I am. I have a master's degree in SWE and am working on a CS-discipline PhD. I am living proof that you don't have to be good at math in order to excel with computers - and I think we do our future generations a huge disservice by forcing them into so much advanced math just to get a degree in computers. But that's a post for another day, I think.)

Tim rocks at math. He can do amazingly complex math in his head. It's something I've alternately envied and despised since we first met. The cool thing is that he can, mostly, explain his methodology and since he did, I've been trying to get better at doing what I call "Tim Math". I don't think his theory is unique - or original - to him. I believe he said one of his elementary school teachers taught them this based on a book or some famous math guy (yeah, I know, very specific - you know, the famous math guy - duh!) Anyway, his methodology is to take the numbers you're dealing with and find numbers that your head can easily play with (like 10 or 5) that are close, and then adjust from that point. It sounds easier than it is (well, at least to me.)

Last night, I was trying to figure out how much was left in a vial of liquid that holds 900 ml. I'd been dispensing 75 ml every night for the last 11 nights. Well, I had no idea what 75 x 11 was and had no desire to go looking around for a calculator. So I thought it was a good opportunity to try some "Tim Math". So my thought process was as follows:

Hm, 75 is close to 100. 100 x 11 is 1100. The difference between 75 and 100 is 25. 25 x 11. Well, 25 x 12 would be 300 because there are 4 25s in 100 and 3 4s in 12. So 25 x 11 would be 25 less than 300, or 275. So if you subtract 275 from 1100 you get 825, so there must be 825 ml left, meaning there is basically one more 75ml serving to dispense.

Very proud of myself, I related this to Tim (since how much was left was an item for discussion previously in the evening.) He just started to chuckle, managing a "Huh" - you know the "Wow, that's a really weird way to have gone about it, but hey if it works for you" kind of "huh". Picking up on this I was slightly deflated and asked, "Well, isn't that how you would do it?"

Tim smiled and said, "Well, actually, I'd have just multipled 75 times 10 and added 75 to that."

Sigh. I'm apparently not even very good at "Tim Math".