Solve Equations

Question

A 625-megabyte CD can record 170 minutes of music. How many minutes can be recorded on 350 megabytes?

Answer 1

This problem can be solved using a proportion (that is, two ratios that are equal).  Be very careful to use units that represent equal ratios (that is, they create a portion). Choose one of these:

 

      MB₁ / min₁ = MB₂ / min₂

      min₁ / MB₁ = min₂ / MB₂

 

      MB₁ / MB₂ = min₁ / min₂

      MB₂ / MB₁ = min₂ / min₁

 

Those ratios all produce the same result when cross-multiplied:

      MB₁ * mn₂ = MB₂ * min₁

 

So,

     ( 625 MB ) / ( 170 min ) = ( 350 MB ) / ( x min )

 

cross-multiply:

      625x = 170*350

        x = 95.2               [divide both sides by 625]

 

95.2 minutes of music may be recorded.