Question

What is a31 of the arithmetic sequence for which a5=3.2 and a9=12.0?

Answer 1

The arithmetic sequence formula:

`a_n=a_1+(n-1)d`

We have:

`a_5=3.2,\ a_9=12.0`

Calculate d (common difference)

`a_9-a_5=4d\\\\4d=12.0-3.2\\\\4d=8.8\ \ \ |:4\\\\d=2.2`

Calculate 31th term:

`a_(31)=a_5+26d\\\\a_(31)=3.2+26\cdot2.2=60.4`