Hints:

1. If fence posts are put in every 7 feet, how many posts are needed to make a 77-foot fence? The intuitive answer is 77/7 = 11 posts. Nope.
2. If it takes a chiming clock 3 seconds to strike 6:00, how long does it take to strike midnight? How many between-chime gaps are there from the first chime to the sixth? Now do the same calculation when it’s striking midnight.
3. Sentence sense. Here are a few more hints.

• The old man the boat. Everyone knows what an “old man” is, but the old can be a noun, and man can be a verb.
• I convinced her children are noisy. Add a word to make it clearer.

4. Where does the length of a year come from? In other words: why is a year 365 days long? The answer is an astronomical phenomenon.
5. Why is it colder in the winter? The earth’s orbit is an ellipse, not a circle, so it does get closer and farther away. The perihelion, the closest point in the earth’s orbit to the sun, is January 3. It couldn’t be that the earth is farthest away during the winter because that would make the entire world have the same seasons, and yet the southern hemisphere has the opposite seasons of the northern.
6. Rowboat drops cannonball into swimming pool. Suppose the cannonball weighs 20 kg. Imagine that we replace it with a 20 kg pellet made of some insanely dense material. How would that change the puzzle?
7. The average IQs of Iowa and Missouri both rise, but both states can’t improve, right? (You were bad, so you get no clue.)
8. Proof that 1 = 2. The clue is in the first step.
9. Fire on the island. Do you have matches in your backpack?
10. Coffee with milk on the side. The rate that hot things lose their heat is proportionate to the temperature difference.
11. Rolling dice. (No clue.)
12. Metal numerals used by homeowners to identify their house number. The obvious answer is that you should make the same number of each numeral. Obviously, that obvious answer is wrong. The clue to a rather profound observation is that streets are finite in length. That means that the house numbers on any particular street will keep on going … until the street ends, and then that series of numbers ends. What does that mean for the digits needed to number those houses?
13. Does the balance tip right, left, or not at all? If you figured out the rowboat and the cannonball, you’ve got the basics to solve this one. The key is to simplify—what elements are significant (in particular: weight and displacement), and which ones can be dismissed?

Answers: