“Fun with Maths at MacDonald’s!”, the random thought popped into my head.
It’s 9:25 p.m., and I haven’t had dinner yet. I’ve just spent the better part of the last hour discussing with Mr Sim how melting ice affects the water level in a container. It’s for one of the questions he’s setting concerning volume. No, it’s not for Science, but Maths. Yes, Mr Sim takes his ‘real-life’ questions to new levels (pun intended).
All that thinking has made me hungry. What scientists say about the brain consuming 20% of the body’s total haul must be true. It takes a few minutes to figure out what I want after flipping through the pages of the virtual menu on the self-order kiosk.
My wish list runs thus:
- 1 McChicken ‘n’ Cheese
- 1 Filet-O-Fish
- 6-piece Chicken McNuggets
- 1 Medium French Fries
- 1 Potato Wedges
- 2 Small Cokes
Figuring out what I want to eat is easy – the challenge is to figure out how best to place my order. Having spent an enervating evening conceptualising ‘real-life’ Maths questions with Mr Sim, I can’t believe what Ronald is putting me through. Another real-life Maths question. Except this is a real-life question, not a real-life one on paper.
These are real-life Math heuristic problem sums that PSLE Math examiners love to set. These questions are the notorious P6 Difficult Math questions. You should train your kids at MacDonald’s, as it makes a difference in pocket money.
Back to the menu – this is how the prices look like for a-la-carte and MacDonald’s Set Menu:
I steal a furtive glance behind me. The coast is clear – no impatient customers peeping over my shoulder.
I make it my mission in life, at least for the next 5 minutes, to find the most cost-efficient way to place my order.
Punching numbers into my phone calculator is not an option; it’s not cool. How best to solve this quickly?
Primary Maths Heuristic – Making A List?
The most direct approach involves listing all the order permutations. In Primary Maths Heuristics, this bulldozer approach is known as (unsurprisingly) ‘Making a List’.
The computation required will look like this:
McChicken ‘n’ Cheese a la carte ($2.60) + Filet-O-Fish with Medium French Fries and Small Coke ($5.00) + 6-piece Chicken McNuggets with Potato Wedges and Small Coke ($6.80) = ?
McChicken ‘n’ Cheese a la carte ($2.60) + Filet-O-Fish with Potato Wedges and Small Coke ($5.80) + 6-piece Chicken McNuggets with Medium French Fries and Small Coke ($6.00) = ?
Filet-O-Fish ($2.50) + McChicken ‘n’ Cheese with Medium French Fries and Small Coke ($5.60) + 6-piece Chicken McNuggets with Potato Wedges and Small Coke ($6.80) = ?
In Maths, three consecutive ellipses means ‘and so the list goes on’. For those who are still with me, you’ve probably figured out that there are 6 possible ways to place my order.
Even if I had enough RAM in my brain to perform the necessary computations and store all the intermediate results, this method doesn’t seem efficient.
Is there a shortcut?
Time to reassess my objective. What I’m really interested in is the cheapest way to place my order. That means what I should be focusing on at this point is the relative price difference among the different combos, and not the absolute total amount.
With this in mind, I scan the price list again. The presence of some round dollar amounts and a healthy ‘number sense’ lead me to discover something. The difference in cost between the Fries + Coke combo and Wedges + Coke combo for all mains is $0.80.
That tells me there is no cost difference between the order configurations below:
Main A a la carte + Main B-Fries-Coke combo + Main C-Wedges-Coke combo
Main A a la carte + Main C-Fries-Coke combo + Main B-Wedges-Coke combo
Thus, the problem is now reduced to identifying the main that I should order a la carte.
I shift my attention to the next type of price difference: main a la carte and Fries-Coke combo (or Wedges-Coke combo).
It’s now clear which main I should order a la carte. If you pick correctly, you should pay only $14.40. If you pick incorrectly, you could end up paying $1.45 more!
Parents, the next time you visit McDonald’s, you might want to delegate the ordering to your children to give them a mental maths workout.
Note to self: To discuss with Mr Sim about adapting this scenario in an upcoming Maths lesson…and if your appetite for MacDonald’s and Math are all fired up, take the MacDonald’s test with their Delivery Orders.
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Related articles:
1. Why are PSLE Math Questions So Hard?
2. How to Help Your Child Improve Composition Writing at Home
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