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32 multiple-choice questions and 15 flashcards on Compound Events, about 21% of the 7th Math: Statistics & Probability bank. Every one carries a written rationale.
Compound Events is one of 5 chapters in CoStudy's 7th Math: Statistics & Probability bank, and it holds 32 of the bank's 150 multiple-choice questions — roughly 21% of the total. That proportion is not arbitrary: chapters follow the certifying body's published exam outline, and the number of questions in each is set by that domain's published weight, so the share of your practice time this chapter takes matches the share of the real exam it accounts for.
Studying by chapter is worth doing once you have a diagnostic score. A single overall percentage tells you whether you are close; it does not tell you which domain is dragging. Working a weak chapter in isolation, and re-testing it in isolation, is the fastest way to move a score that has stalled — and it is why the mock exams in CoStudy report by domain rather than as one number.
2 questions drawn from this chapter, with the full rationale shown — the controlling principle behind the right answer, and why each wrong option tempts and fails.
Which simulation BEST models choosing a random month of the year?
Answer: C — Spinning a 12-section spinner with equal sections
12 equal sections = 12 equal-probability outcomes, matching 12 months. (A) only 2 outcomes; (B) 6 outcomes; (D) 52 cards with unequal category sizes.
For two independent events, which formula gives P(A and B)?
Answer: C — P(A) × P(B)
Independent events: P(A and B) = P(A)·P(B). (A) is OR for mutually exclusive; (B/D) not standard formulas.
4 cards from the 15 in this chapter.
Worked example: P(heads AND rolling a 5) when flipping a coin and rolling a die.
Step 1: Identify the events — A = heads on coin, B = 5 on die. These are independent (one doesn't affect the other). Step 2: Find each probability: P(A) = 1/2, P(B) = 1/6. Step 3: Use the multiplication rule for independent events: P(A and B) = P(A) × P(B). Step 4: Multiply: (1/2)(1/6) = 1/12. Answer: P(heads AND 5) = 1/12.
What is a 'compound event'?
An event made up of two or more events together.
Coin flipped twice. P(at least one head)?
3/4. (4 outcomes total: HH, HT, TH, TT — three have a head.)
Worked example: Simulate a 25% chance event using random digits 0-9.
Step 1: Decide how to map digits. 25% means 25 out of 100 — for 0-9, use 2.5 digits, so we pick 2 digits out of 10 for closest fit (or use 2 digits 00-99). Step 2: Simple choice: let digits 0 and 1 represent 'event occurs' (2 of 10 = 20%, close but not exact). Step 3: Better: use 2-digit pairs 00-99 and let 00-24 = event occurs (exactly 25 of 100 = 25%). Step 4: Generate many trials; count how often the event 'occurs'; divide by total trials to estimate P. Answer: Map 00-24 → event; 25-99 → no event; run 200+ trials and compute relative frequency.
These are a sample. The full Compound Events chapter runs 47 items with per-chapter progress tracking, on the web and in the iOS app.
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