For 30 consecutive days, the daily high temperature was recorded. On each of the first 25 days, the temperature recorded was $21^{\circ} \mathrm{C}$. On each of the remaining 5 days, the temperature recorded was $15^{\circ} \mathrm{C}$. For the 30 days, the mean (average) of the temperatures recorded was
(A) $17^{\circ} \mathrm{C}$
(B) $19^{\circ} \mathrm{C}$
(C) $20^{\circ} \mathrm{C}$
(D) $16^{\circ} \mathrm{C}$
(E) $18^{\circ} \mathrm{C}$
The mean (average) is determined by adding the 30 recorded temperatures, and dividing the sum by 30 .

The sum of the temperatures for the first 25 days was $25 \times 21^{\circ} \mathrm{C}=525^{\circ} \mathrm{C}$.

The sum of the temperatures for the last 5 days was $5 \times 15^{\circ} \mathrm{C}=75^{\circ} \mathrm{C}$.

Thus, the mean of the recorded temperatures was $\frac{525^{\circ} \mathrm{C}+75^{\circ} \mathrm{C}}{30}=\frac{600^{\circ} \mathrm{C}}{30}=20^{\circ} \mathrm{C}$.

ANsWER: (C)