LEARN · EXPLAIN · REVISE

Two strata have mean commute times 20 and 40 minutes and sizes 3k and k. Find the overall mean.

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

TOPIC 01

Statistics: mixed assessment

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

k=9

Skills and prerequisite lessons

Working and explanation

BUILD THE REASONING

Hint 1

State the survey question, population, sampling and measurement rules before drawing a conclusion.

Hint 2

Weight stratum means by their sizes.

Worked solution

State the survey question, population, sampling and measurement rules before drawing a conclusion.
Calculate or simplify this relation.
$\bar x=[20(27)+40(9)]/36=25$
A simple average of the two means would incorrectly ignore the unequal sizes.

The requested value is 25.

Checks and common pitfalls: A simple average of the two means would incorrectly ignore the unequal sizes.

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

Teacher preparation and assessment