The correct preposition here is "among," because "among" is used when referring to more than two things or people that are considered as a group. The election was a fight between multiple parties, so the appropriate preposition is "among."
Thus, the correct preposition is "among," making the sentence: "The election was a straight fight among the four parties."
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?