The square of Mark’s age 3 years ago is 6 times the age he will be in 9 years. What is his age now?
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Question “The square of Mark’s age 3 years ago is 6 times the age he will be in 9 years. What is his age now?”
The square of Mark’s age 3 years ago is 6 times the age he will be in 9 years. What is his age now?
Answer
15 years old
Explanation:
If we denote Mark’s age today by
x
That is what we know.
(x-3)^2
(x+9)
Multiplying is a way to multiply.
(x+9)
(x-3)^2=6(x+9)
This simplifies to a quadratic equation.
x^2-12x-45=0
0=(x-15)(x+3)
These are the possible solutions:
x_1=15
x_2=-3
Evidently, you can’t be under 3 years, so he must have been at least 15 years.
Conclusion
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