If a quantity starts at (70) and decreases by (5) each step, which rule represents it?
Answer and explanation
Correct answer: \(y=70-5x\)
The starting quantity is 70, so when \(x=0\), the value of \(y\) must be 70. Since it decreases by 5 at each step, the coefficient of \(x\) is \(-5\). Therefore, the rule is \(y=70-5x\). In \(y=70+5x\) and \(y=5x+70\), the quantity increases rather than decreases. Exam tip: in a linear rule, the constant term is the initial value, and a decrease has a negative slope.
Frequently asked questions
What is the correct answer to this question?
\(y=70-5x\)
Why is this the correct answer?
The starting quantity is 70, so when \(x=0\), the value of \(y\) must be 70. Since it decreases by 5 at each step, the coefficient of \(x\) is \(-5\). Therefore, the rule is \(y=70-5x\). In \(y=70+5x\) and \(y=5x+70\), the quantity increases rather than decreases. Exam tip: in a linear rule, the constant term is the initial value, and a decrease has a negative slope.
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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