Solve the Problem $\frac { 2 } { 3 }$ As Many Vibrations as in the Previous Second

Multiple Choice

Solve the problem.
-After being struck with a hammer, a gong vibrates 20 vibrations in the first second and in each second thereafter makess $\frac { 2 } { 3 }$ as many vibrations as in the previous second. Find how many vibrations the gong makes before it
Stops vibrating.

A) 30 vibrations
B) 70 vibrations
C) 25 vibrations
D) 60 vibrations