After 20 minutes, Juan had completed 12 questions, which is 0.7 of his assignment. What percent of t

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

We know that 0.7 as a percentage is:
0.7 * 100% = 70%

In this problem, we have either or. Juan either completed the question or DID NOT complete the question.

100% of questions has one of two classifications - Completed or not completed.

This means Juan did not complete the following amount of questions:
100% - 70% = 30%