If (y=90-5x), what is the difference between (y) at (x=2) and (y) at (x=7)?
Answer and explanation
Correct answer: 25
Substituting x=2 gives y=90-5(2)=80. Substituting x=7 gives y=90-5(7)=55. Therefore, the difference between the two y-values is 80-55=25. Here, 5 is the decrease in y for each increase of 1 in x; over an increase of 5 units in x, the total decrease is 5×5=25. Exam tip: For a linear expression, substitute both x-values and subtract the resulting values.
Frequently asked questions
What is the correct answer to this question?
25
Why is this the correct answer?
Substituting x=2 gives y=90-5(2)=80. Substituting x=7 gives y=90-5(7)=55. Therefore, the difference between the two y-values is 80-55=25. Here, 5 is the decrease in y for each increase of 1 in x; over an increase of 5 units in x, the total decrease is 5×5=25. Exam tip: For a linear expression, substitute both x-values and subtract the resulting values.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Introduction to Polynomials. Topic: Linear growth and decay.
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