“Hmm,” said Guido uncertainly. “That’s a bit of a conundrum. By your logic, is appears as if the runner can never catch up to the turtle, for he will only ever cover part of the distance between them. But there must be a trick here, for common sense suggests that a faster runner will eventually catch a slower runner.”
Guido thought for a few chimes and then grabbed a nearby stick. He snapped a piece off the end and measured it to be about a tenth of the size of the original piece. Then, he grabbed two stones a dark one and a light one.
“Suppose the dark pebble is the runner,” he began, laying the stone on the ground. “And this stick is 100 metres.” He lay the stick next to the pebble and then put the lighter stone on the ground at the other end of the stick from the darker one.
“If the runner runs one hundred metres he will end up where the turtle started off. Meanwhile the turtle will have run 10 metres. He moved the dark pebble to where the lighter one was, measured 10 metres with the smaller stick and moved the lighter stone forwards. “So, after the runner runs 100 metres, he is only 10 metres behind.”
“If we repeat this....” He moved the dark pebble forwards by the length of the larger stick and the lighter pebble the length of the smaller stick. “The runner is now well ahead. So, if the total distance travelled by the runner is 200 metres, the turtle would start off 100m ahead but then only cover 20 metres in the time that the runner covered the 200m. So, the turtle would be well beaten in such a race covering 200m.”
He scratched his head. “It must be the way that you posed the problem that creates the conundrum.” He laughed. “But I still can’t work out when he will catch up apart from the fact that it is after 110 metres and before 200 metres.” Guido cupped his head in his hands, thinking deeply.
“Aaah!” He returned the pebbles to where they had been after the first part of the race with the turtle 10 metres ahead. Then, he snapped the two sticks in half. He moved the dark pebble forwards the length of the larger stick and the light one the length of the smaller stick. The dark pebble was well ahead. “So when the runner has covered 150 metres the turtle will only have covered 15 metres plus its start of 100 metres. So, the point where the runner catches up must be before 150 metres, which narrows it down a little more at least. If I could continue snapping these twigs in half, I might eventually find the solution but the twigs would be very small!”
He glanced towards Iasc. “This is a very intriguing problem. I have a feeling you are teaching me some mathematics here. Is my logic in the right direction? Can the problem be solved?”