The last theory we tested was put forward by Fauzi. He believed that during the lunchtime rush, the denomination of notes we used to pay could very possibly have an effect on the amount we’re ultimately charged.

Ben and I didn’t even understand the man, let alone believe him. And so, in another busy hawker centre in the CBD, we found a nasi padang stall with a snaking queue and blindly followed our friend’s instructions.

First, we waited for Fauzi to buy his lunch. It cost him $4.30, which he paid for with a $5 note. He was given 70 cents in change. Ben was next up. He ordered the same meal but he paid with a $10 note. He received one $5 note, one 50 cent coin, and one 20 cent coin.

Then it was my turn. Armed with a $50 note, I stood in line, waited, and eventually bought what my friends did. No big deal, right? Wrong. Counting my change, we discovered I was given $46—four $10 notes and three $2 notes.

So what happened? Did makcik make a mistake in her math? Did she forget the prices of her dishes in a span of just five minutes? Possibly. But she probably just rounded the amount down so it was faster for her to give me my change and get rid of me as quick as possible.

Huh, like that also can ah, I hear you ask. And to that, I say, yes, can.

Yet another lesson you learn in business school is a little thing called queuing theory—a mathematical study of the congestion and delays of waiting in line. In a nutshell, the theory is employed by businesses like banks or fast food restaurants to develop more efficient queuing systems, processes, and arrival management strategies to reduce customer wait times and increase the number of customers served.

TLDR: Long queue = inefficient = slow service = less customers wanting to queue = less $$ made.

If you still don’t quite get the mechanics of queuing theory or understand how it helps businesses, refer to its practical application in McDonald’s. Do you remember a time when you had to actually stand in line at the counter before ordering from a cashier? Do you remember how you got so frustrated at the dude in front of you who waited until it was his turn before deciding what to eat? Or worse, customising his order more than an ah beng zhngs his e-scooter? Do you remember how you got your friend to stand in line in front of a different counter just so either one of you could jump to the one that moved faster?

Compare all that to the numerous self-service kiosks Mcdonalds has today. With the kiosks, everything is more efficient. You go in, tap a few buttons, pay electronically, and wait for your food. Everything takes all of 5 minutes. You still might have to stand in line, but wait times are drastically reduced. McDonald’s can now serve more customers in a shorter time and make more profit.

This change in operational management was no coincidence. It was a result of a careful study of queueing theory.

Makcik also understands the logic behind queuing theory. She knows that it’s in her best interest to keep the line moving. After all, the whole reason behind this article is because Fauzi, Ben, and I didn’t want to waste half our lunch hour standing in line. We wanted to placate our growling stomachs as soon as possible so we headed for the stall with … the shortest queue.

Lest you forget, nasi padang stalls aren’t big enterprises run by huge multinational companies. Makcik doesn’t have 10 helpers working in a production line. At most, she has 2 other relatives/workers. And that’s it. It’s a humble business with a simple business model. Redesigning her operational processes and incorporating technology would just be too time-consuming, not to mention expensive.

This means makcik remains old school, dealing only in cash with no one to help her. She’s perpetually busy and is happiest when you present her with the exact change. When the notes are relatively small, she’ll give you the correct amount back because it doesn’t require much effort. However, if the note is big enough, the queue is long enough, and makcik is busy enough, who knows. You might get lucky. She’ll round it off to save her the time and hassle of fumbling for the right coins.

Think about it for a second: what was a 30 cent loss when she could make another $4 (or more) from the other customers waiting in line? Provided she can keep them in the queue, that is.

Speed is everything.