If y = 220 - 13x, what will be the total decrease in y from x = 4 to x = 9?
Answer and explanation
Correct answer: 65
In y = 220 - 13x, the coefficient -13 represents a decrease of 13 units in y for every one-unit increase in x. The change in x from 4 to 9 is 9 - 4 = 5 units. Thus the total decrease is 13 × 5 = 65 units. Checking by substitution gives y(4) = 168 and y(9) = 103, whose difference is 168 - 103 = 65. Therefore option B is correct. Options A, C, and D arise from multiplying the rate by an incorrect number of x-intervals.
Frequently asked questions
What is the correct answer to this question?
65
Why is this the correct answer?
In y = 220 - 13x, the coefficient -13 represents a decrease of 13 units in y for every one-unit increase in x. The change in x from 4 to 9 is 9 - 4 = 5 units. Thus the total decrease is 13 × 5 = 65 units. Checking by substitution gives y(4) = 168 and y(9) = 103, whose difference is 168 - 103 = 65. Therefore option B is correct. Options A, C, and D arise from multiplying the rate by an incorrect number of x-intervals.
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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