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## Homework Statement

The length of the rod of a certain pendulum is decreased, and the period then decreases by 20%. By how much was the rod length decreased?

## Homework Equations

T=2π√(l/g)

T=period

l=length of the rod

g=acceleration due to gravity

## The Attempt at a Solution

I know how to solve the problem, I just don't know how to do the math to solve for l (length).