3. For many years, one fifth of the houses in a certain city are heated with oil. Currently, an oil company claims that this proportion has decreased. Are we right to doubt this statement? To test this claim, a study was done consisting of a random sample of 1000 houses in that city and it was found that 136 houses are heated by oil.

3. Por muchos anos un quinto de las casas en cierta ciudad se calientan con petroleo. Actualmente, una compania petrolera afirma que esta proporcion ha disminuido. iTenemos razon en dudar de esta afirmacion?. Para probar esta afirmacion se hizo un estudio que consistio de una muestra aleatoria de 1000 casas de esa ciudad y se encontro que 136 casas se calientan con petroleo