B1. Calculate $531+535+539+543+\cdots+983+987$.
B1. The sum of the terms of an arithmetic sequence with a difference of 4 needs to be calculated. The first term is 531, and the last ($n$-th) term is 987. Using the formula for the general term of an arithmetic sequence, we calculate $n=115$. We use the formula for the sum of $n$ terms of an arithmetic sequence and get the sum 87285.

Conclusion: $d=4$. 1 point

Conclusion: $a_{1}=531, a_{n}=987$. 1 point

![](https://cdn.mathpix.com/cropped/2024_06_07_4401d59a37898c9fd2b4g-15.jpg?height=60&width=1637&top_left_y=1506&top_left_x=278)

Result $n=115$ 1 point

Using the formula for the sum of $n$ terms of an arithmetic sequence ... 1 point

Result: $S_{115}=87285$

1 point