Let the duration of each period, when there are 9 periods a day in the school, be x minutes. The following table is obtained.
|Duration of each period (in minutes)||45||x|
|Number of periods||8||9|
If there is more number of periods a day in the school, then the duration of each period will be lesser. Hence, this is a case of inverse proportion.
Therefore 45 × 8 = x × 9
x = (45 x 8)/9 = 40
Hence, in this case, the duration of each period will be 40 minutes.