Discover your age using a simple equation | Age Question Homework Statement"

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The variables are not well chosen; the description is not well stated. If you are just starting out, you should know that many problems will require you to correct the description and then solve the problem.
  • #1
Natasha1
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Homework Statement


Today i am half as old as my brother was 7 years ago. I am 11 years younger than my brother. How old am i?

2. The attempt at a solution
Let I = Me and B = Brother


Let: Brother age = x
Hence my age now = x -11

So, 7 years ago:
my brother was (x - 7)
and I was (x - 11 - 7)

Lets set an equation:
1/2 x I = B
This gives us 1/2 (x - 18) = x - 7
x - 18 = 2x - 14
x = -4

Why do I get a negative age? Can anyone help solve this one please?
 
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  • #2
Natasha1 said:

Homework Statement


Today i am half as old as my brother was 7 years ago. I am 11 years younger than my brother. How old am i?

2. The attempt at a solution
Let I = Me and B = Brother


Let: Brother age = x
Hence my age now = x -11

So, 7 years ago:
my brother was (x - 7)
and I was (x - 11 - 7)

Lets set an equation:
1/2 x I = B
This gives us 1/2 (x - 18) = x - 7
x - 18 = 2x - 14
x = -4

Why do I get a negative age? Can anyone help solve this one please?

It helps to keep things straight (and make your work more readable) if you have two variables: b = brother's current age, m = my current age (both in years). The conditions are that (1) m = (1/2)(b-7); and (2) m = b-11. Try solving these two equations for m and b.
 
  • #3
Natasha1 said:

Homework Statement


Today i am half as old as my brother was 7 years ago. I am 11 years younger than my brother. How old am i?

2. The attempt at a solution
Let I = Me and B = Brother


Let: Brother age = x
Hence my age now = x -11

So, 7 years ago:
my brother was (x - 7)
and I was (x - 11 - 7)

Lets set an equation:
1/2 x I = B
This gives us 1/2 (x - 18) = x - 7
x - 18 = 2x - 14
x = -4

Why do I get a negative age? Can anyone help solve this one please?
You have that your age now is (x − 18), which is right. (See corrections below)

That is (equal to) 1/2 of what your brother's age was 7 years ago: (x − 7)

Which thing should you take 1/2 of ?

Added in Edit: Thanks Chestermiller.
Corrections:
Today you are 11 years younger than your brother (is now)
What is that? Not (x − 18) .
 
Last edited:
  • #4
SammyS said:
You have that your age now is (x − 18), which is right.

That is (equal to)1/2 of what your brother's age was 7 years ago: (x − 7)

Which thing should you take 1/2 of ?
Isn't his age now x-11? Isn't that half of what his brother was 7 years ago (x-7)?
 
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  • #5
I will give a try but my variables choices will be different.
"Me", m
Brother, b

Today i am half as old as my brother was 7 years ago. I am 11 years younger than my brother. How old am i?

m=(1/2)(b-7)
AND
m=b-11

That system of equations is the exact translation of the description, using the variables as I've chosen.
Now, you solve that system, and you get what you get. If bad values result, then the description is at fault.
I have not tried to solve the equations yet.
 
  • #6
Again continuing with the system
m=(1/2)(b-7)
AND
m=b-11

The second equation can give b=m+11.
Substitute into the first equation and solve for m, the number being asked for in the question.
m=4.
and then b=15.

The example problem is a good typical beginners' question.
 

Related to Discover your age using a simple equation | Age Question Homework Statement"

What is the equation used to discover age?

The equation used to discover age is: Age = Current Year - Birth Year.

Is this equation accurate for everyone?

No, this equation is not accurate for everyone. It assumes that the person being tested was born in the same year as the current year, and does not take into account factors such as leap years or time zones.

Can this equation be used for individuals born before the current year?

Yes, this equation can be used for individuals born before the current year. As long as the current year and birth year are known, the equation can be used to calculate age.

Are there any other factors that should be considered when using this equation?

Yes, there are other factors that should be considered when using this equation. It is important to make sure that the current year and birth year are accurate, and that the equation is adjusted for any potential discrepancies, such as leap years or time zones.

Can this equation be used to accurately determine someone's age?

Yes, this equation can be used to accurately determine someone's age under the right circumstances. It is a simple and commonly used method, but may not be entirely accurate for everyone. Other methods, such as using official documents or asking the person directly, may also be necessary for accurate age determination.

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