A bag contains one rupee, 50 paise and 25 paise coins. The ratio of the number of 1 rupee coins to that of 50 paise coins is ` 5 : 9` and the ratio of the number of 50 paise conins to that of 25 paise coins is ` 2 : 1` . Find the value of the 50 paise coins in the bag if the total value of the bag is Rs. 425.