If (N(t)=n-3t) and (N(4)=28), what will (N(9)) be?
Answer and explanation
Correct answer: 13
Given \(N(t)=n-3t\). Substituting \(t=4\), \(N(4)=n-12=28\), so \(n=40\). Now, for \(t=9\), \(N(9)=40-3\times9=40-27=13\). Hence, 13 is correct. A value such as 16 can result from using the rate of decrease or the time value incorrectly. Exam tip: first use the given condition to find the unknown constant \(n\), then substitute the required value of \(t\).
Frequently asked questions
What is the correct answer to this question?
13
Why is this the correct answer?
Given \(N(t)=n-3t\). Substituting \(t=4\), \(N(4)=n-12=28\), so \(n=40\). Now, for \(t=9\), \(N(9)=40-3\times9=40-27=13\). Hence, 13 is correct. A value such as 16 can result from using the rate of decrease or the time value incorrectly. Exam tip: first use the given condition to find the unknown constant \(n\), then substitute the required value of \(t\).
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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