Lesson 4 of 8
Give every case an answer
Show on a big screenThe plan: take the bus if it rains or you are late. Otherwise, walk. Two facts decide it: rain and being late. How many kinds of morning?
Step 1 of 5
- Look outside. Check both facts.
- Raining? Yes: take the bus.
- Late? Yes: take the bus.
- The last No goes nowhere.
- Add an answer: walk.
There are 4 kinds of morning. Each fact can be Yes or No.
The rule
Every case must reach an answer. A case no arrow catches has no answer. Here a case is one kind of morning. No answer means the chart does not say what to do.
Two yes-or-no facts make 4 cases. Three facts make 8. Each new fact doubles the cases. 2 × 2 = 4, then 4 × 2 = 8.
| Raining? | Late? | Answer |
|---|---|---|
| No | No | Walk |
| No | Yes | Bus |
| Yes | No | Bus |
| Yes | Yes | Bus |
Finish the chart. Check all four mornings.
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Try the lab to finish this lesson.