tires and math

Several times in the past month the low tire pressure indicator light has come on just as I pull out of the garage. I'd pull back into the garage and pump up the tire. It was always the same tire. Finally I got around to taking the car into the tire store today.

Turns out that God was really looking out for me. Although the tire with the slow leak was otherwise okay, the other three tires on the car were almost bald. Given the rainy weather we've been having I could have gotten into some serious trouble.

Anyway, what to do with a homeschooled child when stuck at the tire store for a couple of hours? The few pages of work that I stuck on a clipboard wouldn't last long. Instead, I decided to show Sparkle a real-life application of the math she finds so baffling. The salesperson had given me quotes on four different types of replacement tires. Two of the brands were offering rebates of differing amounts. Which set of tires was the best buy?

I explained the problem to Sparkle, and then had her pick out which tires would be cheapest, not including the rebates. Then we figured out how much the tires cost after the rebates. Finally we compared the final costs to determine which was the cheapest set overall.

It was a long process, and I had to guide Sparkle in baby-steps all along the way. (Hey, multi-digit subtraction with borrowing isn't typical first grade math.) However, the math program we use had introduced enough concepts that I was able to break the problem down into manageable chunks.

We didn't bother the other customers in the waiting room too much. The lady sitting next to us was kind enough to ignore our conversation while reading a book. Two other people had nice comments about homeschooling. Texas is great.

Oh, and when we walked out to the car when it was done, Sparkle was thrilled to see that the car sported the brand of tires she had calculated as the cheapest.