Always take the tests under real conditions. Keeping your phone on is definitely not advisable.
7 questions unanswered can result in a huge drop. There is not enough information on how every missed question relates to your score. Also, GMAT prep is the closest
to the real thing. Again, no one is certain (barring the test makers) whether it is the same
Answer to your question: it depends on at what level you were on the test when you missed those questions among other factors. GMAT penalizes you 3 percentile points for every unanswered question.
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