fix: clean-up Project Euler 401-420 (#43028)

curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-411-uphill-paths.md

@@ -8,22 +8,26 @@ dashedName: problem-411-uphill-paths
 
 # --description--
 
-Let n be a positive integer. Suppose there are stations at the coordinates (x, y) = (2i mod n, 3i mod n) for 0 ≤ i ≤ 2n. We will consider stations with the same coordinates as the same station.
+Let $n$ be a positive integer. Suppose there are stations at the coordinates $(x, y) = (2^i\bmod n, 3^i\bmod n)$ for $0 ≤ i ≤ 2n$. We will consider stations with the same coordinates as the same station.
 
-We wish to form a path from (0, 0) to (n, n) such that the x and y coordinates never decrease. Let S(n) be the maximum number of stations such a path can pass through.
+We wish to form a path from (0, 0) to ($n$, $n$) such that the $x$ and $y$ coordinates never decrease.
 
-For example, if n = 22, there are 11 distinct stations, and a valid path can pass through at most 5 stations. Therefore, S(22) = 5. The case is illustrated below, with an example of an optimal path:
+Let $S(n)$ be the maximum number of stations such a path can pass through.
 
-It can also be verified that S(123) = 14 and S(10000) = 48.
+For example, if $n = 22$, there are 11 distinct stations, and a valid path can pass through at most 5 stations. Therefore, $S(22) = 5$. The case is illustrated below, with an example of an optimal path:
 
-Find ∑ S(k5) for 1 ≤ k ≤ 30.
+<img class="img-responsive center-block" alt="valid path passing through 5 stations, for n = 22, with 11 distinct stations" src="https://cdn.freecodecamp.org/curriculum/project-euler/uphill-paths.png" style="background-color: white; padding: 10px;">
+
+It can also be verified that $S(123) = 14$ and $S(10\\,000) = 48$.
+
+Find $\sum S(k^5)$ for $1 ≤ k ≤ 30$.
 
 # --hints--
 
-`euler411()` should return 9936352.
+`uphillPaths()` should return `9936352`.
 
 ```js
-assert.strictEqual(euler411(), 9936352);
+assert.strictEqual(uphillPaths(), 9936352);
 ```
 
 # --seed--
@@ -31,12 +35,12 @@ assert.strictEqual(euler411(), 9936352);
 ## --seed-contents--
 
 ```js
-function euler411() {
+function uphillPaths() {
 
   return true;
 }
 
-euler411();
+uphillPaths();
 ```
 
 # --solutions--