Monday
Monday: Three Straws, One Roof
Rocket lays three straws on the Blueprint Table. "Roof triangle. Four, five and twelve centimeters." He pushes the ends together.
The two short straws lie flat along the long one. The ends never meet. "It will not close!"
"What do you notice about the two short ones?" Raven asks. She lays them end to end beside the long straw.
"Four and five is nine," Rocket says. "The long one is twelve. They cannot reach."
Nova hovers over the straws, her light tracing the gap. "Add the two short ones," she says. "Compare with the longest."
"Six, eight and ten," Raven offers. Rocket tries them. The ends snap together.
"Fourteen beats ten," he says. "Rule found. Write it in the Blueprint Book."
The triangle rule
Three straws make a triangle only when the two shorter straws add to more than the longest one.
Straws 4, 5 and 12: 9 is less than 12, so the ends never meet. No triangle.
Straws 6, 8 and 10: 14 is more than 10, so the ends meet. One triangle.
Straws 3, 4 and 7: 7 equals 7. The short straws lie flat along the long one. Still no triangle.
Why the rule works
Picture the long straw lying on the table. The two short straws start at its ends and swing up to meet.
If together they are shorter than the long straw, they cannot bridge the gap. If they are exactly as long, they lie flat.
Only when they are longer can they lift off the table and meet at a corner.
- Read the question.
- Tap your answer.
- Read the question.
- Tap your answer.
| Statement | True or false? |
|---|---|
| 4 + 5 > 12 | ? |
| 6 + 8 > 10 | ? |
| Straws 3, 4 and 7 cm make a triangle. | ? |
| Any three straws can make a triangle if you push hard enough. | ? |
Write each set in your Blueprint Book with "closes" or "does not close".
Nobody runs with straws or sticks. Straws are tools today, not for drinking.
The rule is found. Tomorrow you learn when three measures fix one triangle, many, or none.