Which pricing strategy innovation most significantly expanded the adoption of advanced mathematics software in universities during the 2000s?

The educational mathematics software industry has undergone significant pricing strategy shifts over the past decades. From early expensive perpetual licenses to today's subscription models, companies have experimented with various approaches to balance accessibility with profitability. This trivia explores a pivotal pricing innovation that revolutionized how advanced mathematical software reached academic institutions.

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Tiered pricing based on institution size (number of enrolled students)
Site licensing with concurrent user limits based on simultaneous connections
Freemium model with basic functions free and advanced features behind paywalls
Pay-per-solution pricing where institutions only paid for successfully completed calculations