Problem - Tandem Bicycle

$n$ red riders with speeds $r_1, .., r_n$ and $n$ blue riders with speeds $b_1, .., b_n$. Each tandem bike has one red and one blue rider. Bike speed = max of the two riders' speeds.

Task $1$: Maximize total speed of all bikes. Task $2$: Minimize total speed of all bikes.

Before reading on, think: how would you pair riders for each task? The core idea: only one rider's speed per bike counts, so you want to avoid wasting fast riders. How you pair them determines whether you use or waste fast speeds.