I need help. With this p

asked Aug 4, 2019 100k views

1 vote

by Xronx

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a_n=a_1+(n-1)d - the formula of n-th term of an arithmetic sequence.

We have:

$a_5=12.4;\ a_9=22.4$

$a_9-a_5=(9-5)d\to4d=22.4-12.4\\\\4d=10\ \ \ \ |:4\\\\d=2.5$

$a_(31)=a_9+(31-9)d\to a_(31)=22.4+22\cdot2.5=77.4$

Answer: C. 77.4

Ozk answered Aug 7, 2019

by Ozk

8.1k points

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