Statistical Analysis
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Two‑population test

Ch 10 · σ known

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Level 2 · Developing Problems auto‑adjust to keep you in the sweet spot — not too easy, not too hard.

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Chapters 10–15
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23 problems · keep the streak alive

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Ch 10 / Two‑population test (σ known)
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The problem

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GreenCart runs two fulfillment centers — North and South. Management wants to know whether they differ in mean order‑processing time (minutes). The population standard deviations are known from historical data. Test, at α = 0.05, whether the means differ.

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GreenCart runs two fulfillment centers — North and South. Do they differ in mean order‑processing time? The population standard deviations are known. Test at α = 0.05.

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Guided mode

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GreenCart compares mean processing time at its North and South centers (σ known). Test at α = 0.05. Fill each step — tap Hint if you get stuck.

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1

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2

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Step‑by‑step solution Two‑population z‑test, σ known
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!

Most common slip here: using σ instead of σ² inside the square root. Always square each standard deviation before dividing by its sample size.

In plain words

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