The correct article to use before "outside" is "an" because the word "outside" starts with a vowel sound. The article "an" is always used before vowel sounds for smoother pronunciation.
The sentence becomes:
If we hurry, there’s still an outside chance of catching the plane.
The correct article is "an".
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?