Wich average is the best for 7,40,42,45,48,50,55

Answer-

Sydney must answer at least 8 questions in the second section to score more than 80 in total.  

Solution-

Worth of each correct answer in the first section = 3 points

Worth of each correct answer in the second section = 5 points

Let us assume that,

x = Number of correct answer from the first section

y = Number of correct answer from the second section

Then total mark scored will be,

As given in the question that she scored more than 80 in the test, so

She correctly answered 15 in the first section, so mark scored in the first section will be 15×3 = 45, then the equation will be

So, she must answer more than 7 questions or at least 8 questions in the second section, in order to score more than 80 in total.