Choose the correct form of the verb that is in agreement with the subject:
30 percent of boys ____ in English in higher secondary examinations.

x percent of plural countable noun + plural verb + plural adjective
Example: 60 percent of the students are boys.
x percent of uncountable noun + singular verb + singular adjective
Example: 21 percent of oxygen is present in the air.
According to the rule and the example that is given above, 'have failed' will be used in the underlined part of the sentence.
Correct sentence: 30 percent of boys have failed in English in higher secondary examinations.