← The Pool Deck Is a Maths Room · Lesson 1 of 4
The clock counts to sixty
A pace clock is a big sweep hand that goes round once a minute. A coach says “ten 50s on the :40” and each swimmer leaves every forty seconds. Because the dial counts to sixty, the leaving places move round it.
On the :40 the swimmer leaves from the top, then the 40, then the 20, then the top again: three places, a triangle. On the :45 it is four places, a square. On 1:35 it is twelve places, a twelve-point star. The rule is the dial divided by what the send-off and sixty share.
Three send-offs, three shapes
A set is on a 1:50 send-off. How many different places on the clock will a swimmer leave from before it repeats?
A lesson is kept once you've answered the question and written at least 8 words. Nobody grades it; it stays on this device.