The exercise type 'Strategy' is meant for answering open mathematical formulas that cover steps in the problem solving in one go.
Exercise type strategy lets the student decide the number of answer fields he wants to use. Every answer field is evaluated agains the same evaluation mechanism. This exercise type can be used (also in tests) if you do not want to prescribe the number of steps/answer fields that the student gets.
Note that you can create a solution rule with evaluation type eval statement and user
length(answers) in it to determine the number of answer fields that were created.
You can use the Number of answer fields dropdown in the General tab to prescribe a minimum number of answer fields a student has to use.