. . . . . . . . eleven year old boy won . . . . . . . . National Essay-writing competition.

Solution (By Examveda Team)

Here, the sentence talks about the 'boy' as general class of things. Since we are referring to general things, we need to use the indefinite article 'a/an'. The word 'eleven' starts with a vowel and therefore 'an' will be used.
In the second blank a specific competition is being talked about. Definite article 'the' will be used.