Question

What is the sum of a 6-term geometric series if the first term is 21 and the last term is 1,240,029?

1,395,030
1,461,460
1,527,890
1,594,320

Answer 1

well you need to find the value of the common ratio. you can do this by using the formula

\[a_{n} = a_{1} \times r^{n - 1}\]

so using the information

\[1240029 = 21\times r^5\]

you need to solve this equation for r

then the sum of 6 terms is

\[s_{6} = \frac{21( 1 - r^6)}{1 - r}\]