21. The manager of a grocery store asks Kamar to construct a display consisting of 10 rows of cans stacked on top of each other. The manager wants the bottom row to have 25 cans and each succeeding row to have I less can than the row below it. Part of 3 rows of the display is shown in the figure below. How many cans will be in the top row of the display?
Your Answer is
Correct Answer is C
Explanation
It is known that the first item is 25, the difference is -1, and there are 10 items in total, then according to the arithmetic sequence formula, the 10th item is S10=S1+ (n-1)×d can get S10=25+(10-1)×(-1)=16, so choose C