Consider a ballet dancer executing pirouettes with rotations of: 1.5, 2.5, and 3.5 revolutions about a vertical axis while in the air. The dancer remains airborne for roughly 0.70 seconds. Initially, the dancer leaps into the air with arms and legs extended in an "open" position with an initial moment of inertia of I₀ and a rotational frequency 𝑓₀ = 1.2 rev/s, maintaining this for 0.10 s. Next, the dancer pulls in their limbs towards their body, which reduces their inertia to 𝐼 and achieves a rotational frequency of 𝑓 which is sustained for 0.50 s. Lastly, the dancer returns to the "open" position for 0.10 s until landing on the ground. Calculate the minimum rotational frequency 𝑓 during the middle phase of the jump to ensure that the dancer completes a single and a triple pirouette successfully.