Dirt bikes let you ride up and down hills, zoom off ramps and flip upside-down. Surfing lets you soar through the air as ocean waves push you. So how about doing both at the same time? As we see in this video, famous dirt biker Robbie Maddison built a bike that drives on water. When he pedals, he paddles, because that back tire works like a big paddlewheel from an old steamer boat. The bike also has water skis on the sides to help it float. The skis are just above the bottoms of the tires, so the bike can roll right onto the shore and keep driving on land!

*Wee ones:* If the bike has 2 wheels plus that paddlewheel, how many wheels does it have in total?

*Little kids:* If you can pedal-paddle the boat bike 9 miles an hour and row a regular boat 5 miles an hour, which one is faster? *Bonus:* How much faster is the boat bike?

*Big kids:* It took Robbie 2 1/2 years to build this bike. If he finished in August, in what month did he start? *Bonus:* If he then rides it for another 2 1/2 years from that time, in what month would that take him to?

Answers:

*Wee ones:* 3 wheels.

*Little kids:* The boat bike. *Bonus:* 4 miles an hour faster.

*Big kids:* In February. *Bonus:* In February, again, because an even 2 years would take him to August again.