The function is , where is the month and represents January.

Find the average rate of change for each time interval.

(a) April to May

represents April and represents May.

The interval is .

Average rate of change of  on the interval .

Average rate of change of  on the interval .

The rate represents per month; the average temparature increases from early spring to mid-spring.

(b) July to November

represents July and represents November.

The interval is .

Average rate of change of  on the interval .

The rate represents per month; the average temparature decreases from summer to late autumn.

(a) per month; the average temparature increases from early spring to mid-spring.

(b) per month; the average temparature decreases from summer to late autumn.