How to accurately calculate the root n degree of number

For example, it is necessary to calculate the root of the 3rd degree out of 27000. I recorded the following ways

  a =  pow  ( 27000 ,  1 / 3 ) # The answer is approximately 29.99999993  a =  27000  ** ( 1 / 3 ) # answer the same      
 tried to use the fractions module, but the answer It does not change. How to find an exact number, if there is such an opportunity. Rounding is not desirable