The first term of an arithmetic sequence is 200. The common difference is -10. Find the value of 20th term.
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10
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d = -10, a = 200
a20 = a + (20 -1) d = 200 + (19 × - 10) = 200 -190 = 10
The first term of an arithmetic sequence is 5 and the common difference is 2. Find the sum of its first 25 terms.