0, 1, or in between
Every chance is a number from 0 to 1. It is never less than 0. It is never more than 1.
Step 1 of 4
- A line from 0 to 1.
- 0 means it can never happen. 1 means it will surely happen.
- Most chances sit in between, like 3/8.
- 3/2 or −0.2 are off the line. Something was counted wrong.
Two new words
- Impossible event — it can never happen. P = 0. Example: a 7 on one die with faces 1 to 6.
- Sure event — it always happens. P = 1. Example: a number below 7 on that die.
So for any event E: 0 ≤ P(E) ≤ 1.
Why? The wanted outcomes are part of all the outcomes. A part is never bigger than the whole.
Fix wrong answers by counting again
| Wrong answer | The mistake | Right answer |
|---|---|---|
| Spinner 1 to 4: P(1, 2, 3 or 4) = 6/4 | only 4 parts, not 6 | 4/4 = 1 |
| Spinner 1 to 4: P(5) = −0.2 | no part shows 5 | 0/4 = 0 |
| Paper slips 1 to 10: P(multiple of 4) = 3/10, "4, 8, 44" | there is no slip 44 | 2/10 = 1/5 |
Watch out!
"3/10 is between 0 and 1" is not enough. A wrong count can land there too. The line catches only big mistakes. Count again.
Now try it. Count first. Then tap: sure, impossible, or in between.
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