Let the total number of questions in the exam be 100.
# of multiple choice questions= 60
# of subjective questions= 40 ("rests were subjective")
Out of 40 subjective questions, 30 are Subjective-B and 10 are Subjective-A. ("30% of all questions were subjective questions in category B": 30% of 100 questions)
Jack answered all category B questions --> He answered 30 of the subjective questions and did not answer 10 of the subjective questions.
We have to find 10 is what percent of 40.
40*(x/100)=10 ==> x=25
Answer: B

Given:
1. jack appeared for an examination that had only two categories of difficulty levels, category A that had all difficult questions and category B that had all moderate difficulty level questions.
2. 60% of the total questions in the paper were multiple choice and rests were subjective
3. only 30% of all questions were subjective questions in category B.

Asked: If Jack answered to the category B questions only, what percentage of the subjective questions were not answered by Lampard?

Multiple choice questions = 60%
Subjective questions = 40%

Subjective questions in category B = 30%
Subjective questions in category A = 40%-30%=10%

Since Jack answered to category B questions only, he left 10% subjective questions of category A

Percentage of subjective questions not answered by Jack = 10/40= 25%

My predicament is that it doesn't say 30% of ALL questions are subjective. Typically with all these sums, we take a percentage or fraction of the total in that particular category.

Posted from my mobile device

Out of 40 subjective questions, 30 are Subjective-B and 10 are Subjective-A. ("30% of all questions were subjective questions in category B": 30% of 100 questions)