2025 SSMO Relay Round 4 Problems

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Problem 1

Call a positive integer chuzzed if the sum of the digits in its binary representation is equal to the units digit of its base-$10$ representation. Similarly, call a positive integer chopped if its binary representation does not contain two consecutive ones. Find the number of positive integers less than $128$ that are chuzzed and chopped.

Solution

Problem 2

Let $T = TNYWR.$ Jonathan and Kate are playing a game with $n$ sticks. On each turn, a player may remove $1,$ $2,$ or $3$ sticks. The player who picks up the last stick loses. Kate is first to remove sticks, and both players play optimally. For how many values of $n$ in the range $\left[T^3,2T^3\right]$ does Kate have a winning strategy?

Solution

Problem 3

Let $T = TNYWR.$ A particle moves in the coordinate plane such that at any time $t,$ its position is \[\left(\sum_{a=1}^{T-1} \cos(at),\sum_{a=1}^{T-1} \sin(at)\right).\] Over the time interval $t\in(0,k],$ the particle lies on at least one coordinate axes $T$ times. If the minimal value of $k$ can be written as $\frac{m\pi}{n}$ for relatively prime positive integers $m$ and $n,$ find $m+n$.

Solution