If there are 6 periods in each working day of a school, then the number of ways that you can arrange 5 subjects during the working day is

Since there are 6 periods and 5 subjects in each working day, one subject must be repeated. This subject can be selected from the five subjects in ${ }^5{C}_1=5$ ways. In each section there are 6 subjects in which one subject repeated 2 times. These can be arranged in $\frac{6!}{2!}=\frac{720}{2}=360way$  
$\therefore$ The number of required arrangements $=5\times 360=1800$