Probability of an Event (Grade 7)
When an event can happen in several ways, count all the favorable outcomes and divide by the total.
Understanding probability of an event from a spinner
On a spinner split into 8 equal sectors, the probability of landing on an even number is (how many even sectors) / 8. Always simplify the fraction at the end.
Seeing it in action
Worked example
A spinner has 8 equal sectors numbered 1–8. P(even)?
Even sectors: 2, 4, 6, 8 → 4 favorable. Total = 8.
P(even) = 4/8 = 1/2.
Count every favorable sector, then simplify.
A common mistake, and the fix
Counting the favorable outcomes but not dividing by the total, or not simplifying.
On 8 equal sectors numbered 1 to 8, the even numbers are 2, 4, 6 and 8: 4 out of 8, which is 4/8 = 1/2.
Try a few
Sectors 1–6, P(greater than 4)?
5, 6.
Sectors 1–10, P(a multiple of 3)?
3, 6, 9.
Sectors 1–8, P(less than 3)?
1, 2.
Spinner
A calm probability game for reading spinner sectors, fractions, complements, and comparisons.
Try it in Numeris.
A short lesson, then practice with feedback on every answer.
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