Find the sum 25 + 28 +31 + ... + 100 .
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Answer:A=25
d=28−25=3
an=100
an=a+(n−1)d
100=25+(n−1)(3)
100−25=(n−1)(3)
75=(n−1)(3)
75/3=(n−1)
25=(n−1)
25+1=n
26=n
Sn =n/2(a+an)
=26/2(25+100)
=13(125)
=1625
Step-by-step explanation:
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