Ten pairs of jeans. Six white, four black. What percentage are black?

I use that kind of simple problem in this video because the PISA conversation can become so large that we lose sight of what understanding actually looks like. A ranking becomes a political fight. Meanwhile, can a teenager explain a fraction of a total?

The answer is 40%. The explanation matters more than guessing the number.

Do the calculation in the open

There are 6 + 4 = 10 pairs altogether. Four of those ten are black. Divide the part by the whole, then multiply by 100:

4 ÷ 10 × 100 = 40%.

The other six are 60%. Together, 40% + 60% = 100%. That last check helps reveal whether the calculation describes the whole collection.

The part and the whole. White: 6 of 10: 60%; Black: 4 of 10: 40%; White: 6 of 12: 50%; Black: 6 of 12: 50%
Illustrative jeans example, before and after adding two black pairs.

Now change the collection. Add two more black pairs. There are six black pairs out of twelve, so 6 ÷ 12 × 100 = 50%. The total changed along with the part. Adding two to the numerator while leaving ten underneath would answer the wrong question.

This extends the example in my clip. It is not presented as an official PISA test item, nor as evidence that a particular percentage of students failed this exact question.

What the published results say

Kosovo’s mean mathematics score was 350 in PISA 2025, compared with 355 in 2022: a numerical difference of −5 score points. The ministry reports reading at 340 versus 342 and science at 357 in both cycles. ¹

Kosovo mathematics scores. PISA 2022: 355 points; PISA 2025: 350 points
Ministry figures. Difference: −5 score points; not an IQ or percentage scale.

These are assessment-score differences. They are not percentages of intelligence lost. The OECD characterises mathematics as declining while reading and science were approximately unchanged. ²

The anger in my recording reaches teachers, parents and political decisions. None of those frustrations alone establishes the cause of the score. A national assessment is a signal to investigate teaching and learning, not evidence that a named person failed their duties.

For the broader comparison, see the PISA results article. For a practical family response, see what a parent can do tonight.

Ask where the explanation breaks

A student may know a rule and still struggle to recognise when to use it. Another may understand the idea but make an arithmetic error. Those are different problems and deserve different help.

Ask the learner to identify the whole. Then the part. Then what would happen if the whole changed. Give them room to explain without turning the exercise into humiliation.

This is why I keep returning to elementary examples. I want education to become something visible in a person’s reasoning, not only something printed on a certificate.

Four out of ten is a small place to start. Start there, and find out what the child actually understands.

Sources and calculation notes

  • ¹ Kosovo Ministry: publication of PISA 2025 results, 8 September 2026. Changes calculated as 2025 minus 2022: mathematics 350 − 355 = −5; reading 340 − 342 = −2; science 357 − 357 = 0.

  • ² OECD: PISA 2025, Kosovo, interpretation of changes. The assessment concerns students around age 15, not every resident’s general intelligence.

  • Jeans example: 4/(6+4) × 100 = 40%; after adding two black pairs, 6/(6+6) × 100 = 50%. Inputs and results. The extended example is illustrative. Country comparisons and causal claims in the spoken commentary are not treated as independently established findings here.

  • Original video and thumbnail: Eduard Luta on TikTok. Published 2026-09-08. Research checked 26 September 2026.