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← The Pool Deck Is a Maths Room · Lesson 4 of 4

The smaller number wins

About it

Almost everywhere else, a bigger number is better. In a race it is the other way round: faster means less, and a “drop” is good news. Percent change is measured on a number that is shrinking.

Then the World Aquatics points table turns it back: a smaller time earns more points. Saying the flip out loud — at home, on the deck — saves years of sign mistakes.

The figure

In a race, left is better

56606468beforeaftera drop: good news← fasterslower →
A number line of seconds. Faster times sit to the left and slower to the right, so the arrow from 1:05.32 to 58.90 points left: the number got smaller, and that is the good news.
One question

A swimmer goes from 40.00 to 38.00. By what percent did the time drop?

Say it back
A lesson is kept once you've answered the question and written at least 8 words. Nobody grades it; it stays on this device.