Question

一道很简单的sat数学题！

The first term in the sequence above us a, and each term after the first is 3 times the preceeding term. If the sum of the first 5 terms is 605, what is the value of a?

Answer 1

a1=n, an=3*a(n-1)
s5=a1+a2+a3+a4+a5=605
a1=5
the value of a is 5

Answer 2

a+3a+9a+27a+81a=121a=605 so a=5