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21 multiple-choice questions and 12 flashcards on Comparing Two Populations Informally, about 14% of the 7th Math: Statistics & Probability bank. Every one carries a written rationale.
Comparing Two Populations Informally is one of 5 chapters in CoStudy's 7th Math: Statistics & Probability bank, and it holds 21 of the bank's 150 multiple-choice questions — roughly 14% 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.
10 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.
Two random samples of 7th-grade boys and girls measure heights. The mean difference (boys − girls) is +0.5 inches; both groups have MAD of about 2 inches. Best inference:
Answer: B — The typical difference (0.5 in.) is small compared to within-group spread (2 in.) — the difference is not very meaningful
Mean diff much smaller than typical within-group spread → weak evidence of a meaningful gap. (A) overreach; (C) ignores the small diff; (D) wrong.
The probability of an event that is certain is:
Answer: C — 1
Probability ranges from 0 (impossible) to 1 (certain). An event that always happens has probability 1. (A) is impossible; (B) is equally likely; (D) no probability exceeds 1.
Two MAP scores show School A (mean 75, MAD 5) and School B (mean 75, MAD 15). School B's scores are:
Answer: B — More variable (larger MAD)
B) Larger MAD means more spread. A) Opposite. C) Means match. D) MAD differs.
You flip a coin 200 times and get 94 heads. Experimental P(heads):
Answer: B — 0.47
Experimental probability = 94/200 = 0.47. (A) is theoretical; (C) is 106/200; (D) is the difference from 0.50.
Class A: mean = 85, MAD = 3. Class B: mean = 85, MAD = 9. Which statement is best supported?
Answer: A — Class A scores are more consistent than Class B
Same mean, smaller MAD = tighter clustering. (B) means are equal; (C) MAD says nothing about count; (D) MADs differ.
The sample space for flipping a coin and rolling a die has how many outcomes?
Answer: D — 12
2 coin outcomes × 6 die outcomes = 12. (A) only coin; (B) only die; (C) 2 + 6 = 8 (incorrect addition).
You spin a 5-section spinner with sections 1–5. P(odd number)?
Answer: D — 3/5
Odd numbers: 1, 3, 5 → 3 outcomes / 5 total = 3/5. (A) is P(even); (C) is one outcome; (B) wrong denominator.
Two distributions have the same mean and same MAD. Can you conclude they are identical?
Answer: D — No — shape (skew, modes) can still differ
Center and spread don't fully describe a distribution — shape can differ. (A) too strong; (B/C) not sufficient either.
A bag contains 4 red and 6 blue marbles. The probability of picking a red marble is:
Answer: B — 4/10
P(red) = favorable / total = 4/10 = 2/5. (A) is red:blue ratio, not probability; (C) is P(blue); (D) is 1 out of 4.
A dot plot of class A is symmetric and centered at 8; class B is right-skewed centered near 5 with a few high values. Best inference:
Answer: A — Class A has a higher typical value and is more symmetric
Symmetric center 8 vs. skewed center 5: A is higher and more symmetric. (B) typical value of B is lower; (C) shapes differ; (D) spread is visible.
3 cards from the 12 in this chapter.
For mutually exclusive events 'OR', what do you do?
ADD probabilities. P(A or B) = P(A) + P(B).
What does 'fair' mean for a die?
Each face is equally likely (P = 1/6 each).
What's the relationship between P(event) and P(not event)?
They sum to 1. P(not E) = 1 − P(E).
These are a sample. The full Comparing Two Populations Informally chapter runs 33 items with per-chapter progress tracking, on the web and in the iOS app.
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