Question

the sum of 8 and 18term of arithmetic sequence is 80
a) find the sum of first and 25th term
b) what is the sum of first 25terms
c) find the 13term of the sequence

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Answer 1

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• A + (n-1) d = a(n)
• a(8)+a(18) =80
• a+7d+a+17d=80
• 2(a+12d)=80
• a+12d=40
• 13th term = 40

Answer 2

Step-by-step explanation:

a)a+a+24d=2a+24d

=2(a+12d)

=2(40)=80

b)n/2(2a+(n-1)d)

25/2 (2a+24d)

25/2 (2*40)

25/2 (80)

25*40

1000

And:1000

c)40