Question

If there are $5$ periods in each working day of a school, then find the number of ways that you can arrange $4$ subjects during the working day.

• A. $220$
• B. $240$
• C. $260$
• D. $280$

Answer 1

The correct option is B $240$

There are 5 periods and 4 subjects, then it means that one subject is being repeated.

Select one subject from the 5 in ${}^5{C}_1$ ways and this set can be arranged in $\frac{5!}{2!}$ ways.

So total number of ways ${=}^5{C}_1\times \frac{5!}{2!}=240$