The square of a number is 2800 more than 30 times the number. What is the positive number?
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Answer and explanation
Correct answer: 70
Let the number be \(x\). Then \(x^2=30x+2800\), so \(x^2-30x-2800=0\). Factoring gives \((x-70)(x+40)=0\), hence \(x=70\) or \(x=-40\). Since the question asks for the positive number, the answer is 70. In an exam, find both roots and then apply the condition stated in the question, such as positivity.
Frequently asked questions
What is the correct answer to this question?
70
Why is this the correct answer?
Let the number be \(x\). Then \(x^2=30x+2800\), so \(x^2-30x-2800=0\). Factoring gives \((x-70)(x+40)=0\), hence \(x=70\) or \(x=-40\). Since the question asks for the positive number, the answer is 70. In an exam, find both roots and then apply the condition stated in the question, such as positivity.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Quadratic Equations. Topic: Word Problems and Applications.
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