1. **Stating the problem:** We want to find the formula for the number $N$ of employees needed to perform an activity $n$ times during a work day of duration $T$, given that each activity takes time $t$ and the capacity utilisation is $a$ percent. 2. **Understanding the variables:** - $t$: time to perform one activity - $n$: number of times the activity is performed in a day - $T$: total duration of the work day - $a$: capacity utilisation in percent - $N$: number of employees needed 3. **Formula derivation:** The total time required for all activities in a day is $n \times t$. The total available time per employee, considering capacity utilisation $a$, is $T \times \frac{a}{100}$. Therefore, the number of employees needed is the total required time divided by the available time per employee: $$ N = \frac{n \times t}{T \times \frac{a}{100}} = \frac{n \times t \times 100}{T \times a} $$ 4. **Explanation:** - Multiply $n$ and $t$ to get total activity time. - Multiply $T$ by $\frac{a}{100}$ to get effective working time per employee. - Divide total activity time by effective working time per employee to get $N$. 5. **Matching with given options:** The correct formula is: $$ N = \frac{n \times t \times 100}{T \times a} $$ which corresponds to the fourth formula option. **Final answer:** $$ N = \frac{n \times t \times 100}{T \times a} $$