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When 399 is added to the square of a number, the result is 3208. What is the positive number?
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Answer and explanation
Correct answer: 53
Let the number be x. Then x² + 399 = 3208, so x² = 3208 − 399 = 2809. Since 2809 = 53², x = ±53; therefore, the required positive number is 53. Exam tip: Taking a square root gives both signs, but select the positive value when the question asks for a positive number.
Frequently asked questions
What is the correct answer to this question?
53
Why is this the correct answer?
Let the number be x. Then x² + 399 = 3208, so x² = 3208 − 399 = 2809. Since 2809 = 53², x = ±53; therefore, the required positive number is 53. Exam tip: Taking a square root gives both signs, but select the positive value when the question asks for a positive number.
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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