Can the Hare Beat the Tortoise?
Given his ability to outpace Tortoise by 25%, the mathematically minded Hare wants to minimize his margin of victory over his longtime foe. The magical racetrack expands proportionally by 10 miles instantaneously at each minute. Based on the magically expanding track length, Hare wants to know:
How long after the race has begun should Hare wait so that both Tortoise and Hare will cross the finish line at the same exact moment?
First, we will figure out how long it will take Tortoise to finish. To do so, since the total length is dynamic but expands proportionally, we will instead focus on the ratio of the track completed at time t. The total track length is F(t)=10(1+⌊t⌋).
Thus, while the Tortoise's speed may be fixed at 60 mph with respect to a fixed vantage point, Tortoise's closing speed with respect to the track length is vT(t)=1miles / minuteF(t)miles / track=110(1+⌊t⌋)track / minute. Tortoise will then finish the track at time τ such that ∫τ0vT(t)dt=⌊τ⌋∑k=0110(k+1)+τ−⌊τ⌋10(1+⌈τ⌉)=1. Ignoring the ceilings and floors, gives us roughly 110Hτ+1≈ln(τ+1)+γ10=1, so τ≈⌈e10−γ⌉−1=12366 where γ=0.57721.... is the Euler-Mascheroni constant. Root solving further gives τ=12365.4681....
Knowing when Tortoise will complete the track allows our very mathematically inclined Hare to back into when he should start. Hare's relative velocity is vH(t)=32(1+⌊t⌋), if t≥t0 and vH(t)=0 if t≤t0. So then we need to find t0 such that ∫τ0vH(t)dt=∫τt0vH(t)dt=3(⌈t0⌉−t0)20(1+⌊t0⌋)+⌊τ⌋∑k=⌈t0⌉320(k+1)+3(τ−⌊τ⌋)20(1+⌈τ⌉)=1. If we ignore the first and last terms then we have approximately 320lnτt0≈1, which should give t0≈τe−20/3≈15. Root solving further gives t0=15.2416....minutes.
Turns out that my estimate for how when the turtle would finish was off by 1 minute, not such a big deal in the scheme of several days. However, I made Hare much faster than he should have been. He should have had relative velocity of 5/4 * v_Tortoise rather than 3/2 * v_Tortoise. Updating that puts the estimated time at around 4 minutes, which is relatively close to the real solution of 3 minutes 40 seconds as per https://fivethirtyeight.com/features/are-you-a-pinball-wizard/
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