Question

What is the sum of this geometric series?

16 + 24 + ... + 81

Answer 1

first you need to know that it looks like
\[a+ar+ar^2+ar^3+...\]
\(a=16\) which is easy because it is the first number
\[r=\frac{24}{16}=\frac{3}{2}\]

Answer 2

now you can either use a formula, or you can use a calculator and figure out what all the terms are

Answer 3

\[16+24+36+54+81\] and we know this because to get from one number to the next you multiply by \(\frac{3}{2}\)

Answer 4

so i add then together and then multiply? or i just add them together?