Three counted buckets show probability as selected count over the same total. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Bucket row 1 uses count over total
Bucket 0 has selected count 1 out of total 4, so the probability is 1/4.
P(bucket 0)=41=41
Bucket row 2 uses count over total
Bucket 1 has selected count 2 out of total 4, so the probability is 1/2.
P(bucket 1)=42=21
Bucket row 3 uses count over total
Bucket 2 has selected count 1 out of total 4, so the probability is 1/4.
P(bucket 2)=41=41
Probability follows selected count over the same total
The total stays four. Counts one, two, and one give probabilities one fourth, one half, and one fourth.