diff --git a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-329-prime-frog.md b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-329-prime-frog.md
index e14df07e58a..8bc5d23be19 100644
--- a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-329-prime-frog.md
+++ b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-329-prime-frog.md
@@ -25,7 +25,7 @@ Give your answer as a string as a fraction `p/q` in reduced form.
 `primeFrog()` should return a string.
 
 ```js
-assert(typeof primeFrog() === 'string');
+asset.isString(primeFrog());
 ```
 
 `primeFrog()` should return the string `199740353/29386561536000`.
diff --git a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-336-maximix-arrangements.md b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-336-maximix-arrangements.md
index 95f2a7ecd37..63a5bbb7b92 100644
--- a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-336-maximix-arrangements.md
+++ b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-336-maximix-arrangements.md
@@ -29,7 +29,7 @@ Find the ${2011}^{\text{th}}$ lexicographic maximix arrangement for eleven carri
 `maximixArrangements()` should return a string.
 
 ```js
-assert(typeof maximixArrangements() === 'string');
+asset.isString(maximixArrangements());
 ```
 
 `maximixArrangements()` should return the string `CAGBIHEFJDK`.
diff --git a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-380-amazing-mazes.md b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-380-amazing-mazes.md
index b44804a15a3..210dc21e505 100644
--- a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-380-amazing-mazes.md
+++ b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-380-amazing-mazes.md
@@ -25,7 +25,7 @@ When giving your answer, use a lowercase e to separate mantissa and exponent. E.
 `amazingMazes()` should return a string.
 
 ```js
-assert(typeof amazingMazes() === 'string');
+asset.isString(amazingMazes());
 ```
 
 `amazingMazes()` should return the string `6.3202e25093`.
diff --git a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-399-squarefree-fibonacci-numbers.md b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-399-squarefree-fibonacci-numbers.md
index 37a34ad1549..24239f0ddc6 100644
--- a/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-399-squarefree-fibonacci-numbers.md
+++ b/curriculum/challenges/english/18-project-euler/project-euler-problems-301-to-400/problem-399-squarefree-fibonacci-numbers.md
@@ -31,7 +31,7 @@ If it happens that the conjecture is false, then the accepted answer to this pro
 `squarefreeFibonacciNumbers()` should return a string.
 
 ```js
-assert(typeof squarefreeFibonacciNumbers() === 'string');
+asset.isString(squarefreeFibonacciNumbers());
 ```
 
 `squarefreeFibonacciNumbers()` should return the string `1508395636674243,6.5e27330467`.