Did you know that our highways — the really big interstate ones — all follow a code? Look at the ones that stretch across the whole US: I-90 runs from Seattle to Boston, I-80 from northern California to New Jersey, and I-10 from southern California to Florida. Notice that all those numbers are even: east-west interstates get even numbers, and north-south ones get odds. The major ones are also multiples of 5, so those cross-country ones are multiples of 10. Better yet, the highways are lined up in numerical order. Small east-west numbers start way south in Florida, ending with I-90 and other high numbers way up north. I-5 in the West runs through Washington, Oregon and California, while I-95 runs down the East Coast. With over 46,000 miles of interstates, we need a good way to keep track.
Wee ones: If you were numbering interstates in order, what number would come after I-5?
Little kids: Can you name all the numbers from 1 to 10 that could be east-west (even) interstate numbers? Bonus: Can you name all the multiples of 10 from I-10 to I-90?
Big kids: I-90 is the longest interstate at 3,020 miles, and the 2nd-longest is I-80 at about 2,900 miles. About how much longer is I-90? Bonus: On the big highway signs for interstates, that little blue and red shield is 3 feet tall! It looks tiny only because it’s so high up. How much taller than that shield symbol are you, in inches?
Wee ones: I-6.
Little kids: They will be the even numbers: 2, 4, 6, 8, and 10. Bonus: I-20, I-30, I-40, I-50, I-60, I-70, and I-80. But there’s no real I-50 or I-60, since they’d run right near the US highways with those numbers.
Big kids: 120 miles longer. Bonus: Different for everyone… find your height in inches and subtract 36 inches, since that is 3 feet.
Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.