Question

After 20 minutes Juan had completed 12 questions, which is 0.7 of his assignment. What percent of the assignment had Juan not completed?

Answer 1

Are you sure it's not 0.6 instead of 0.7? 

If it's 0.7, then he has not completed 30% of his assignment.
If it's 0.6, then he has not completed 40% of his assignment.