Answer:
Jack omitted 5 questions
Step-by-step explanation:
There are 20 questions
7 points given for each correct answer
2 points deducted for each wrong answer
0 for each question omitted.
Jack scored 87 points.
Maximum points Jack could get is 20*7=140 points
Let's use trial and error.
Let Jack answered 13 correct, 2 wrong and 5 omitted
So, 13*7=91
2*-2=-4
So, 91-4=87
Jack omitted 5 questions.