In an arithmetic sequence with 25 terms, if the first term is 60 and last term i...
Question
In an arithmetic sequence with 25 terms, if the first term is 60 and last term is -12, the sum of the terms of the sequence isOptions
A) 600
B) 2400
C) 900
D) 1800
The correct answer is A.
Explanation:
\(-12=60 + (25-1)d\)
\(24d= -72\)
\(d=-3\)
\(s=\cfrac{n}{2}(2a + (n-1)d)\)
\(\cfrac{25}{2}(2 \times 60 + (25-1)-3)\)
\(\cfrac{25}{2}(120-72)\)
\(\cfrac{25}{2}(48)\)
\(=600\)
Explanation provided by Uwakwe Chukwuemeka
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\(-12=60 + (25-1)d\)
\(24d= -72\)
\(d=-3\)
\(s=\cfrac{n}{2}(2a + (n-1)d)\)
\(\cfrac{25}{2}(2 \times 60 + (25-1)-3)\)
\(\cfrac{25}{2}(120-72)\)
\(\cfrac{25}{2}(48)\)
\(=600\)