If a bird flies at a rate of 2/3 of a mile per minute, then at how many miles per hour is it flying?

 

  If a bird flies at a rate of 2/3 of a mile per minute,     

  then at how many miles per hour is it flying?      

 

  We're going to use cancellation of units to make sure we divide     

  when we're supposed to, and multiply when we're supposed to.     

 

                             ²/₃ ^mile/_minute • ⁶⁰/₁ ^minute/_hour  =     

 

  cancel "minutes" to obtain    (²/₃ • ⁶⁰/₁) ^mile/_hour  =     

 

                                                        ¹²⁰/₃ ^mile/_hour  =  40 miles per hour     

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