LEARN · EXPLAIN · REVISE

From t red and 3 blue balls, select 2 without replacement. Find the probability exactly one is red.

Read the idea, work independently, then explain what changed.

TOPIC 01

Random variables and distributions: mixed review

A mixed assessment: identify the method, justify it and revise your reasoning.

Use one hint at a time. A correction explains what changed, not just the final answer.

01 / Standard#Your turn

t=28

Binomial trials have fixed n, common p and independence; hypergeometric sampling uses a finite population without replacement.

Skills and prerequisite lessons

Working and explanation

BUILD THE REASONING

Hint 1

Express the event with a conditional probability or a disjoint partition.

Hint 2

Use this intermediate relation.

C_t^1C_3^1/C_{t+3}^2

Worked solution

The requested value is 0.18064516129.

Checks and common pitfalls: Choose one from each color; do not add a spurious ordering factor.

Think first. Reveal a hint when the class is ready.

Teacher preparation and assessment