During a 90-day monsoon season, daily rainfall can be modeled by sinusoidal functions. A low of 4 inches of rainfall was recorded on day 30, and overall the average daily rainfall was 8 inches. During what period was daily rainfall less than 5 inches?

Step-by-step explanation:

Let consider the following model:

The average is given by the following formula:

The maximum value is:

Amplitude is:

The sine function has a periodicity of , where is minimum is reached at , when t = 30.  The period of the cycle is:

The complete expression is:

The times associated with are, respectively:

Instants are, respectively:

Period is:

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