AP Statistics 3.15.A Expected Counts in Two-Way Tables

Practise calculating expected counts in two-way tables from row, column, and grand totals, then using them to evaluate chi-square cell contributions.

Exam points

Calculate an expected cell count as row total times column total divided by grand total.
Keep expected counts as model-based values; they do not have to be whole numbers.
Use expected counts to form a cell's chi-square contribution from observed-minus-expected.

[Maximum number: 1]

Questions 6-8 refer to the following situation: A computer manufacturer sets up three locations to provide technical support for its customers. Logs are kept, noting whether or not calls about problems are solved successfully. Data from a sample of 1,000 calls are summarized in the following table:

Table for Question 3.15.A—Calculate expected counts for two-way tables of categorical data question 1 — AP Statistics

Assuming there is no association between location and whether or not a problem is resolved successfully, what is the expected number of successful calls (problem solved) from location 1?

$\frac{(325)(450)}{700}$

$\frac{(450)(700)}{1,000}$

$\frac{(325)(700)}{450}$

$\frac{(325)(700)}{1,000}$

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3.15.A—Calculate expected counts for two-way tables of categorical data question 1