From the Department of Very Curious Math
RAY: Here's the answer. They were riding on their 21-speed bicycles. A 21-speed bike has three sprockets in the front and seven in the back. Seven times three is 21, right? So, one and six is when you mesh the first gear with the sixth gear, that's sixth gear, and then two and five is not ten but in fact it's 12th gear, and three and three is seventeenth gear.
So who's our winner?
TOM: The winner is Sam Wheeler from Jericho, Vermont.
[ Car Talk Puzzler ]