You are serving as the only cashier at a supermarket. But there's no queue: instead, after you

finish processing a customer, you decide which customer to process next.

Every minute, a customer arrives at your checkout: $10\%$ of the time, they have a big basket,

which takes $5$ minutes to process. Otherwise, they have a small basket, which takes $30$ seconds

to process.

Can you come up with a strategy that processes customers both efficiently and fairly? Feel

free to create and solve your own extensions and variants!