Thursday

Raven opens the Blueprint Book to the straw page. "Six sets. Three closed, three did not. What do you notice?"

"The ones that failed all had one long straw," Rocket says. "Twelve, seven, twelve."

"Not just long," Raven says. "Longer than the other two together. Or equal, for 3, 4 and 7."

Nova hovers above the page, her light resting on the 5, 9, 9 row. "Two equal straws," she says. "What kind of roof is that?"

"A pointy one," Rocket says. "Both slopes the same. I like that one."

"Then that is our roof," Raven says. "Five across, nine up each side."

Rocket is already cutting more straws. "One triangle for every wall."

Nova hums. "Same three straws, same triangle, every time."

The crew's own six sets, in centimeters, with the rule worked out for each one.

The two right-hand columns always match. That is the rule at work: 3 sets closed, and 3 did not.

The set 3, 4, 7 is the sneaky one. The short pair equals the longest, and equal is not enough.

The roof set 5, 9, 9 has two equal straws. It makes exactly one triangle, the same for every wall.

A roof of four such triangles on a square base is a pyramid. The crew will slice a clay one again tomorrow.

Three sides fix each triangle, so four copies of 5, 9, 9 all match. That is what makes the roof fit together.

The roof set is chosen. Tomorrow you find triangle rules and slices around the house and review the week.