The relation **Employees**(EmpID, DeptID, Salary, Age) contains 1 200 tuples.

- There are 10 departments, each containing the same number of employees.
- Salary distribution: 30 % earn less than $\text{₦}50\,000$, 50 % earn between $\text{₦}50\,000$ and $\text{₦}100\,000$, and 20 % earn more than $\text{₦}100\,000$.
- Age distribution: 40 % are under 30 years, 35 % are between 30 and 45 years, and 25 % are over 45 years.

Assuming that salary and age categories are independent,

(a) How many employees earn between $\text{₦}50\,000$ and $\text{₦}100\,000$ **and** are over 45 years old?

(b) Write a relational algebra expression that retrieves the **EmpID** of those employees.

Question

The relation **Employees**(EmpID, DeptID, Salary, Age) contains 1 200 tuples.

- There are 10 departments, each containing the same number of employees.
- Salary distribution: 30 % earn less than $\text{₦}50\,000$, 50 % earn between $\text{₦}50\,000$ and $\text{₦}100\,000$, and 20 % earn more than $\text{₦}100\,000$.
- Age distribution: 40 % are under 30 years, 35 % are between 30 and 45 years, and 25 % are over 45 years.

Assuming that salary and age categories are independent,

(a) How many employees earn between $\text{₦}50\,000$ and $\text{₦}100\,000$ **and** are over 45 years old?

(b) Write a relational algebra expression that retrieves the **EmpID** of those employees.

Accepted Answer

150 employees; $\pi_{EmpID}(\sigma_{Salary \ge 50000 \land Salary \le 100000 \land Age > 45}(Employees))$

Neco 2022 Data Processing Question 43

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