fifty       
number uk/ˈfɪf.ti/ us/ˈfɪf.ti/
A2 (数字)50
the number 50
  forty-nine, fifty, fifty-one 49,50,51 
 "How fast were they driving?" "They were doing fifty (miles an hour)." “他们当时开得有多快?”“他们的时速达到了50英里。” 
 - More examples
 - Although never married, they lived together as husband and wife for fifty years.
 - Although the film was made fifty years ago, it has lost none of its magic.
 - This car does about fifty miles to the gallon.
 - You should see her wardrobe - it's unbelievable - she's got about fifty pairs of shoes.
 - There are about fifty calories in an apple.