PSAT Math Grid-Ins Question 122: Answer and Explanation
Question: 122
If x > 0 and x2 + 10x = 11 , what is the value of x + 5?
Correct Answer: 6
Explanation:
6 Look for a way to seamlessly make the original expression a variation of x + 5. Add 25 to both sides of the equation x2 + 10x = 11 to form x2 + 10x + 25 = 36. The result can be expressed as (x + 5)2 = 36 . Therefore, x + 5 = 6. Alternatively, you could determine the value of x using the quadratic formula, 
. However, this will be more labor intensive than if you use the shortcut.
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