How Old is John Now Based on Past and Future Age Calculations?

[harpazo]

Homework Statement

Find John's current age using algebra.

Relevant Equations

x - 5 = (1/2)(x + 8)

Five years ago, John’s age was half of the age he will be in 8 years. How old is he now?

John's age now = x
John's age 5 years ago = x - 5
John's age in 8 years = x + 8

x - 5 = (1/2)(x + 8)

x - 5 = (x/2) + 4

2(x - 5) = 2[(x/2) + 4]

2x - 10 = x + 8

2x - x = 8 + 10

x = 18

John is currently 18 years old.

Let me check.

Let x = 18

18 - 5 = (1/2)(18 + 8)

13 = (1/2)(26)

13 = 13

It checks to be true.

 

[BvU]

​

impeccable !

 

[harpazo]

​

impeccable !

Not too bad. Of course, word problems will get increasingly harder as the weeks and months go on.

 

[BvU]

Be assured PF is there to help !

$\$

 

[harpazo]

Be assured PF is there to help !

$\$

I really hope so. There are questions that I simply will not even know how to begin, which is pretty common.

 

[symbolipoint]

Homework Statement:: Find John's current age using algebra.
Relevant Equations:: x - 5 = (1/2)(x + 8)

Five years ago, John’s age was half of the age he will be in 8 years. How old is he now?

John's age now = x
John's age 5 years ago = x - 5
John's age in 8 years = x + 8

x - 5 = (1/2)(x + 8)

x - 5 = (x/2) + 4

2(x - 5) = 2[(x/2) + 4]

2x - 10 = x + 8

2x - x = 8 + 10

x = 18

John is currently 18 years old.

Let me check.

Let x = 18

18 - 5 = (1/2)(18 + 8)

13 = (1/2)(26)

13 = 13

It checks to be true.

I looked at this for the question and setup. It looks good; but I did not look carefully at the algebraic solving steps. I have not yet looked at the posts which followed.

 

[harpazo]

I looked at this for the question and setup. It looks good; but I did not look carefully at the algebraic solving steps. I have not yet looked at the posts which followed.

I hope to be right.

 

[harpazo]

YOU ARE NOW ON MY IGNORE LIST.

 

[BvU]

Very bad idea!

 

[harpazo]

Very bad idea!

Why?

 

[jbriggs444]

Why?

Apparently it has a side effect of putting a strike-through effect on one's name. Strange.

 

[symbolipoint]

YOU ARE NOW ON MY IGNORE LIST.

Who? Me? I am just trying to help!