If (U(t)=150-15t), when will (U(t)=45)?
Answer and explanation
Correct answer: \(t=7\)
Given \(U(t)=150-15t\), put \(U(t)=45\). This gives \(150-15t=45\), so \(-15t=-105\) and hence \(t=7\). If \(t=9\), the value is \(15\), not 45. Exam tip: In linear decay questions, substitute the target value into the function and solve the resulting equation for \(t\).
Frequently asked questions
What is the correct answer to this question?
\(t=7\)
Why is this the correct answer?
Given \(U(t)=150-15t\), put \(U(t)=45\). This gives \(150-15t=45\), so \(-15t=-105\) and hence \(t=7\). If \(t=9\), the value is \(15\), not 45. Exam tip: In linear decay questions, substitute the target value into the function and solve the resulting equation for \(t\).
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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