Let Excel’s Solver do the heavy math!

HOW DO WE SOLVE THIS PUZZLE?  I’m 7 times as old as Lisa is now. In 20 years Lisa will be just half the age I will be then. How old is Lisa now?


The Puzzle









I saw this puzzle recently. I had to really concentrate…I solved it by substituting numbers.

In the business world these puzzles are more challenging. What can we do?

  • Write an Algebra equation?
  • Call a Data Scientist?

The secret is using Excel’s Solver Add-In!



What Are We Solving?

What we’re solving is:  How old is Lisa now?

Get the Excel file here.



What Do We Know?

Let’s start with the facts. We don’t know Lisa’s age yet but we do know:

  • Dad is 7 times as old as Lisa is now
  • In 20 years Lisa will be half dad’s age.

For now we’ll simply type in a 7 and a 20 as seen below.







Add Simple Formulas

I put 9 in cell L12 so the formulas would populate.

Cells L17, L18 and L19 have these formulas:

  • =IF(L12=””,””,L12*L14)
  • =IF(L12=””,””,L12+L15)
  • =IF(L12=””,””,L17+L15)













Solver Magic

Look at red cell L21. It should be a 2 (Dad’s future age double Lisa’s future age).

Yes we can adjust Lisa’s current age in cell L12 but in a more complex case this could take hours!

Let’s use Solver! (Never used solver? See solver tutorial link below)

Solver set-up:

  • cell L21 formula result must be a 2 (Dad’s age double Lisa’s age)
  • change Lisa’s current age (cell L12) until cell L21 = 2
  • cell L12 must be an integer (whole number)



















Solver Results!

Solver has solved the puzzle for us! Press “OK” to accept the solution!












So….Lisa’s current age is 4 !  














Solver Tutorial !

Solver is one of Excel’s secret weapons!

Here is an excellent solver tutorial from Svetlana Cheusheva at ablebits.com








About Me

I’m Kevin Lehrbass. I’m a Data Analyst from Markham Ontario. This was me in Montreal at a nice Polish restaurant called Stash Cafe.

Data tools have really evolved since I started working with data in 2001. Excel has DAX and M (also used in Power BI !) and just this week I heard about some amazing new Excel functions called Dynamic Arrays! Read Bill Jelen’s post Filter Excel Data with a Function  and get his free PDF!

1 Comment Let Excel’s Solver do the heavy math!

  1. Pingback: Excel Roundup 20181025 – Contextures Blog

Leave a Reply

Your email address will not be published.