How to Calculate an unknown number?
 

I want to know how to calculate an unknown number based on facts.
I'm basically trying to perform algebraic equations with excel.
Could someone give me a hand with this theoretical question:
A man, when asked by his niece how old he was, replied, "My age is now four
times yours, but five years ago it was five times yours." How old was he?

This just needs some algebra:

(1) y = 4x

(2) y - 5 = 5 (x - 5)

Substituting, distributing, and rearranging:

(3) y = 5 (x - 5) + 5

(4) 4x = 5x - 25 + 5

So:

(5) x = 20

and

(6) y = 80


One way, using XL:

A2: =4 * A1
A3: =5 * (A1 - 5) + 5
A4: =A3 - A2

Choose Tools/Goal Seek. Enter:

Set cell: A4
To value: 0
by changing cell: A1

and click OK.


In article ,
"Beau" wrote:

I want to know how to calculate an unknown number based on facts.
I'm basically trying to perform algebraic equations with excel.
Could someone give me a hand with this theoretical question:
A man, when asked by his niece how old he was, replied, "My age is now four
times yours, but five years ago it was five times yours." How old was he?