CNA: The PSLE Math problem that got everyone calculating – and asking

In my CNA app today (Sunday October 3, 2021), I read an article about a math test problem that reportedly caused immense distress among test-takers and their parents…plus caused a wave of reactions on social media. The story “The PSLE Math problem that got everyone calculating – and asking Why do Helen and Ivan have so much change when everyone’s gone cashless?” was written by Khoo Bee Khim.

The test question as reported in the article was…

Helen and Ivan had the same number of coins. Helen had a number of 50-cent coins, and 64 20-cent coins. These coins had a mass of 1.134kg. Ivan had a number of 50-cent coins and 104 20-cent coins.

1) Who has more money in coins and by how much?

2) Given that each 50-cent coin is 2.7g more heavier than a 20-cent coin, what is the mass of Ivan’s coins in kilograms?

I gave a go at solving the problem. I initially started on a spreadsheet then moved to a pen and paper (and calculator). I scribbled an equality expression and after 10 minutes reached an answer for part 1 when I realized it wasn’t an equality problem. Then I contemplated an approach to part 2 and set up an equality expression for that and reached an answer. My answer for part 1 was correct, but I had done an addition when a subtraction was called for in part 2 and had the wrong answer initially. Switching the addition to a subtraction got the correct answer. I am an average C-student after all.

After this experience, I feel this was a fair question and showed which students had high organizational thinking skills. There are other factors in play as well though. These include:

(1) the ability to interpret story-based questions. We know that girls tend to do better in this area.

(2) the comfort with unknowns. Most students are conditioned to be able to manage two unknowns in a problem: x and y. This two-part question had three unknowns in part 2, but one of them was already expressed in part 1. There was sequential dependency. So the issue here was the perceived high uncertainty because the problem had two parts. In coding, we might call this nested logic.

(3) tracking units. Some students may have got the wrong answer in part 2 because weight information was given in kg and g. This is a classic “trick” in STEM problem solving.

(4) test context. If this question was considered part of the “hardest” part of the test, then perhaps we could assume most of the rest was…less hard? There is also strategy in where this and other “hardest” questions were placed in the test…beginning…middle…or end. This would be the stamina and change of pace factors. In the real world, if this problem was the only one that needed to be solved in day, how many people would be successful?

(5) test balance. Was this question building on a previous problem that tested a similar math skill but in a simpler context? Ever had a test where every single question was “hardest” and filled with booby-traps? I have…once.

In relation to what we discuss in YCISL, I wonder whether students will ever need this particular math solving skill? And after answering that, will the educational system ever help students to become masters at solving this type of problem?

Furthermore, this question is outright positioned on the reasoning side of thinking skills. The storyline set-up is a distraction and perhaps a creativity decoy. There are many ways to make this a creativity-testing question or even a real world type question. Maybe one day, our tests will advance to that more emotionally intelligent level.

Love the Instagrams really though…!

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