The 8th term of an arithmetic sequence is 40. Calculate the sum of the first 5 terms
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Step-by-step explanation:
given that a8=40
a+7d=40.......…(1)
s5= 5/2 (2a+4d)
=5/2(80-14d+4d)
=5/2(80-10d)
=5(40-5d)
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