Basic Probability — Likelihood of an Event (Grades 6–7)
Probability measures how likely something is, as a fraction from 0 (impossible) to 1 (certain).
Understanding basic probability
For equally-likely outcomes, the probability of an event is the number of favorable outcomes divided by the total number of outcomes. Flipping a fair coin, P(heads) = 1 favorable / 2 total = 1/2.
Seeing it in action
Worked example
A bag has 2 red and 4 blue marbles. P(red)?
Favorable (red) = 2; total = 2 + 4 = 6.
P(red) = 2/6 = 1/3.
Probability = favorable outcomes / total outcomes.
A common mistake, and the fix
Comparing the favorable outcomes with the unfavorable ones instead of with the total.
With 2 red and 4 blue marbles, P(red) is 2 out of 6, which simplifies to 1/3, not 2/4. The bottom of the fraction counts every marble.
Try a few
A fair die: P(rolling a 3)?
5 red, 5 green: P(green)?
Spinner with 4 equal parts, 1 gold: P(gold)?
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.
Put the reasoning on paper.
Try six fraction, angle, perimeter and area questions with explained answers, for grades 4–6.
Free printable · 3 pagesText version (screen-reader friendly): Draw it. Explain it. Math sample
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