Example

Guitar String Frequency and Length: An Inverse Variation Application

Problem: The frequency of a guitar string varies inversely with its length. A 26-inch string has a frequency of 440 vibrations per second. (a) Write the equation of variation. (b) How many vibrations per second will there be if the string's length is reduced to 20 inches by placing a finger on a fret?

Part (a) — Find the equation.

Let ff = frequency and LL = length. Because ff varies inversely with LL, write the inverse variation formula:

f=kLf = \frac{k}{L}

Substitute the known values f=440f = 440 and L=26L = 26:

440=k26440 = \frac{k}{26}

Solve for the constant of variation by multiplying both sides by 26:

26440=k26 \cdot 440 = k

k=11,440k = 11{,}440

Substitute kk back into the formula:

f=11,440Lf = \frac{11{,}440}{L}

Part (b) — Find ff when L=20L = 20.

Substitute L=20L = 20 into the equation:

f=11,44020=572f = \frac{11{,}440}{20} = 572

A 20-inch guitar string has a frequency of 572 vibrations per second. Shortening the string from 26 inches to 20 inches increases the frequency from 440 to 572, which is consistent with the inverse relationship: a shorter string vibrates more rapidly.

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Updated 2026-05-01

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