10/2 (2a+9d) = 255
20/2 (2a+19d) = 1010
solve for a and d, and then you want x such that
255 + x = 30/2 (2a+29d)
The sum of the first ten terms of an a.p is 255. Find the sum of the next 20 term of the progression given that the sum of the first twenty term of the progression is 1010
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