A person travels 84 km in x hours at a speed of (x+5) km/h. What is the value of x?
Answer and explanation
Correct answer: 7 hours
Using distance = speed × time, we get \(x(x+5)=84\). Thus, \(x^2+5x-84=0\), which factors as \((x+12)(x-7)=0\). Therefore, \(x=-12\) or \(x=7\). Since time cannot be negative, the valid answer is 7 hours. Exam tip: Reject any negative root when the variable represents time or distance.
Frequently asked questions
What is the correct answer to this question?
7 hours
Why is this the correct answer?
Using distance = speed × time, we get \(x(x+5)=84\). Thus, \(x^2+5x-84=0\), which factors as \((x+12)(x-7)=0\). Therefore, \(x=-12\) or \(x=7\). Since time cannot be negative, the valid answer is 7 hours. Exam tip: Reject any negative root when the variable represents time or distance.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Quadratic Equations. Topic: Word Problems and Applications.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
