Let x be the no. of $0.20 stamps and y be the number of $0.30 stamps
St. 1 : Insufficient - Total no. of stamps is unknown
St. 2 : Insufficient - 0.2x + 0.3y = 2.50. The possible values of (x,y) include (5,5), (8,3), (11,1)
St. 1 & 2 : Sufficient - x = y and 0.2x + 0.3y = 2.50. hence, x=y=5.
"Success is going from failure to failure without a loss of enthusiam." - Winston Churchill
As vs Like - Check this link : http://www.grammar-quizzes.com/like-as.html.