10. A gardener is planting 7 rows of trees in a triangular plot. The first row contains 1 tree. Each successive row contains 2 more trees than the previous row. How many trees will the gardener plant in the triangular plot?

Answer and Explanation

Your Answer is

Correct Answer is J

Explanation

Treat tree planting as an arithmetic sequence whose first term is 1 and tolerance is 2, and find the sum of the first 7 terms. First, the last item is calculated as 1+(7-1)×2=13, and (1+13)×7÷2=49 is obtained according to the summation formula “(first item + last item) × number of items ÷ 2”.