If (C(t)=180-7t) and (D(t)=60+5t), at what (t) will (C(t)) be (12) less than (D(t))?
Answer and explanation
Correct answer: (t = 11)
“12 less than (D(t))” means (C(t)=D(t)-12). Therefore, (180-7t=60+5t-12). Simplifying gives (180-7t=48+5t), so (132=12t) and hence (t=11). Therefore, option C is correct. At (t=10), the difference between the two functions is not 12. Exam tip: In “less than” questions, subtract the stated difference from the reference expression first.
Frequently asked questions
What is the correct answer to this question?
(t = 11)
Why is this the correct answer?
“12 less than (D(t))” means (C(t)=D(t)-12). Therefore, (180-7t=60+5t-12). Simplifying gives (180-7t=48+5t), so (132=12t) and hence (t=11). Therefore, option C is correct. At (t=10), the difference between the two functions is not 12. Exam tip: In “less than” questions, subtract the stated difference from the reference expression first.
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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