I found this on http://www.playwithyourmath.com/ and adapted it a little.

The number 25 can be broken up in many ways, like 1+4+4+7+9

Let’s multiply the parts together, getting 504 (or something near)

Problem 1: Find the break-up which gives the max product of the parts. 1+1+1+…+1 is not much use.

Problem 2: Find a rule for doing this for any whole number.

Problem 3: Put this rule in the form of a computer algorithm (pseudocode is OK)

Problem 4: Write the rule as a single calculation (formula)