When 9 times a number is added to the square of the number, the result is 400. What is the positive number?
Answer and explanation
Correct answer: 16
Let the number be \(x\). Then \(x^2+9x=400\), or \(x^2+9x-400=0\). Factoring gives \((x-16)(x+25)=0\), so \(x=16\) or \(x=-25\). Since the question asks for the positive number, the answer is 16. Exam tip: Find both roots of the quadratic and then apply the condition specified in the question.
Frequently asked questions
What is the correct answer to this question?
16
Why is this the correct answer?
Let the number be \(x\). Then \(x^2+9x=400\), or \(x^2+9x-400=0\). Factoring gives \((x-16)(x+25)=0\), so \(x=16\) or \(x=-25\). Since the question asks for the positive number, the answer is 16. Exam tip: Find both roots of the quadratic and then apply the condition specified in the question.
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.
