Interactive picture of probability as a count: a row of equally likely outcomes with the favourable ones lit, and a 0-to-1 line showing the fraction
Before it is a number, a probability is a count
Nobody picks a probability. When every outcome has the same chance, you count how many outcomes you want and compare that with how many there are: that fraction is the probability. Raise the favourable count and watch the row light up and the marker move along the 0-to-1 line; then raise the total and watch the same count shrink into a smaller fraction.
Counted probability
P(A) = 0.33
Change the favourable count, then change the total. Before each change, call the new decimal and check it against the line.
P(A) = 2/6 = 0.33
Total outcomes6
24681012
Favourable outcomes2
Favourable ÷ total
1/3
2/6 = 0.33
P(not A)
2/3
4/6 = 0.67
Which rule the paragraph explains
Know This
When every outcome is equally likely, P(A) = favourable outcomes ÷ total outcomes, a value that always sits between 0 and 1.