diff --git a/src/038-unions-and-narrowing/039-combining-unions.problem.ts b/src/038-unions-and-narrowing/039-combining-unions.problem.ts
new file mode 100644
index 0000000..2bcc3d6
--- /dev/null
+++ b/src/038-unions-and-narrowing/039-combining-unions.problem.ts
@@ -0,0 +1,21 @@
+type HttpCode = "400" | "401" | "404" | "500" | "200" | "201" | "204";
+
+const handleErrorCase = (code: string) => {
+  // An imaginary function where we only handle the errors
+
+  type test = Expect<Equal<typeof code, "400" | "401" | "404" | "500">>;
+};
+
+const handleSuccessCase = (code: string) => {
+  // An imaginary function where we only handle the success cases
+
+  type test = Expect<Equal<typeof code, "200" | "201" | "204">>;
+};
+
+const handleAllCase = (code: HttpCode) => {
+  // An imaginary function where we handle all the cases
+
+  type test = Expect<
+    Equal<typeof code, "200" | "201" | "204" | "400" | "401" | "404" | "500">
+  >;
+};
diff --git a/src/038-unions-and-narrowing/039-combining-unions.solution.ts b/src/038-unions-and-narrowing/039-combining-unions.solution.ts
new file mode 100644
index 0000000..374c7f0
--- /dev/null
+++ b/src/038-unions-and-narrowing/039-combining-unions.solution.ts
@@ -0,0 +1,24 @@
+type SuccessCode = "200" | "201" | "204";
+type ErrorCode = "400" | "401" | "404" | "500";
+
+type HttpCode = SuccessCode | ErrorCode;
+
+const handleErrorCase = (code: ErrorCode) => {
+  // An imaginary function where we only handle the errors
+
+  type test = Expect<Equal<typeof code, "400" | "401" | "404" | "500">>;
+};
+
+const handleSuccessCase = (code: SuccessCode) => {
+  // An imaginary function where we only handle the success cases
+
+  type test = Expect<Equal<typeof code, "200" | "201" | "204">>;
+};
+
+const handleAllCase = (code: HttpCode) => {
+  // An imaginary function where we handle all the cases
+
+  type test = Expect<
+    Equal<typeof code, "200" | "201" | "204" | "400" | "401" | "404" | "500">
+  >;
+};
diff --git a/src/038-unions-and-narrowing/039-how-big-can-a-union-be.explainer.ts b/src/038-unions-and-narrowing/040-how-big-can-a-union-be.explainer.ts
similarity index 100%
rename from src/038-unions-and-narrowing/039-how-big-can-a-union-be.explainer.ts
rename to src/038-unions-and-narrowing/040-how-big-can-a-union-be.explainer.ts
diff --git a/src/038-unions-and-narrowing/040-literals-vs-wider-types.explainer.ts b/src/038-unions-and-narrowing/041-literals-vs-wider-types.explainer.ts
similarity index 100%
rename from src/038-unions-and-narrowing/040-literals-vs-wider-types.explainer.ts
rename to src/038-unions-and-narrowing/041-literals-vs-wider-types.explainer.ts
diff --git a/src/038-unions-and-narrowing/041-narrowing-unions-with-typeof.explainer.ts b/src/038-unions-and-narrowing/042-narrowing-unions-with-typeof.explainer.ts
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rename from src/038-unions-and-narrowing/041-narrowing-unions-with-typeof.explainer.ts
rename to src/038-unions-and-narrowing/042-narrowing-unions-with-typeof.explainer.ts
diff --git a/src/038-unions-and-narrowing/042-narrowing-with-if-statements.problem.ts b/src/038-unions-and-narrowing/043-narrowing-with-if-statements.problem.ts
similarity index 100%
rename from src/038-unions-and-narrowing/042-narrowing-with-if-statements.problem.ts
rename to src/038-unions-and-narrowing/043-narrowing-with-if-statements.problem.ts
diff --git a/src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.1.ts b/src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.1.ts
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rename from src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.1.ts
rename to src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.1.ts
diff --git a/src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.2.ts b/src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.2.ts
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rename from src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.2.ts
rename to src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.2.ts
diff --git a/src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.3.ts b/src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.3.ts
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rename from src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.3.ts
rename to src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.3.ts
diff --git a/src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.4.ts b/src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.4.ts
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rename from src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.4.ts
rename to src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.4.ts
diff --git a/src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.5.ts b/src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.5.ts
similarity index 100%
rename from src/038-unions-and-narrowing/042-narrowing-with-if-statements.solution.5.ts
rename to src/038-unions-and-narrowing/043-narrowing-with-if-statements.solution.5.ts
diff --git a/src/038-unions-and-narrowing/043-narrowing-with-boolean-wont-work.explainer.ts b/src/038-unions-and-narrowing/044-narrowing-with-boolean-wont-work.explainer.ts
similarity index 100%
rename from src/038-unions-and-narrowing/043-narrowing-with-boolean-wont-work.explainer.ts
rename to src/038-unions-and-narrowing/044-narrowing-with-boolean-wont-work.explainer.ts
diff --git a/src/038-unions-and-narrowing/044-throwing-errors-to-narrow.problem.ts b/src/038-unions-and-narrowing/045-throwing-errors-to-narrow.problem.ts
similarity index 100%
rename from src/038-unions-and-narrowing/044-throwing-errors-to-narrow.problem.ts
rename to src/038-unions-and-narrowing/045-throwing-errors-to-narrow.problem.ts
diff --git a/src/038-unions-and-narrowing/044-throwing-errors-to-narrow.solution.ts b/src/038-unions-and-narrowing/045-throwing-errors-to-narrow.solution.ts
similarity index 100%
rename from src/038-unions-and-narrowing/044-throwing-errors-to-narrow.solution.ts
rename to src/038-unions-and-narrowing/045-throwing-errors-to-narrow.solution.ts
diff --git a/src/038-unions-and-narrowing/045-narrowing-with-instanceof-statements.problem.ts b/src/038-unions-and-narrowing/046-narrowing-with-instanceof-statements.problem.ts
similarity index 100%
rename from src/038-unions-and-narrowing/045-narrowing-with-instanceof-statements.problem.ts
rename to src/038-unions-and-narrowing/046-narrowing-with-instanceof-statements.problem.ts
diff --git a/src/038-unions-and-narrowing/045-narrowing-with-instanceof-statements.solution.ts b/src/038-unions-and-narrowing/046-narrowing-with-instanceof-statements.solution.ts
similarity index 100%
rename from src/038-unions-and-narrowing/045-narrowing-with-instanceof-statements.solution.ts
rename to src/038-unions-and-narrowing/046-narrowing-with-instanceof-statements.solution.ts
diff --git a/src/038-unions-and-narrowing/046-narrowing-with-in-statements.problem.ts b/src/038-unions-and-narrowing/047-narrowing-with-in-statements.problem.ts
similarity index 100%
rename from src/038-unions-and-narrowing/046-narrowing-with-in-statements.problem.ts
rename to src/038-unions-and-narrowing/047-narrowing-with-in-statements.problem.ts
diff --git a/src/038-unions-and-narrowing/046-narrowing-with-in-statements.solution.ts b/src/038-unions-and-narrowing/047-narrowing-with-in-statements.solution.ts
similarity index 100%
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diff --git a/src/038-unions-and-narrowing/047-narrowing-unknown-to-a-value.problem.ts b/src/038-unions-and-narrowing/048-narrowing-unknown-to-a-value.problem.ts
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rename from src/038-unions-and-narrowing/047-narrowing-unknown-to-a-value.problem.ts
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diff --git a/src/038-unions-and-narrowing/047-narrowing-unknown-to-a-value.solution.ts b/src/038-unions-and-narrowing/048-narrowing-unknown-to-a-value.solution.ts
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diff --git a/src/038-unions-and-narrowing/048-narrowing-with-ternaries.problem.ts b/src/038-unions-and-narrowing/049-narrowing-with-ternaries.problem.ts
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diff --git a/src/038-unions-and-narrowing/049-narrowing-with-nullish-coalescing.problem.ts b/src/038-unions-and-narrowing/050-narrowing-with-nullish-coalescing.problem.ts
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diff --git a/src/038-unions-and-narrowing/049-narrowing-with-nullish-coalescing.solution.ts b/src/038-unions-and-narrowing/050-narrowing-with-nullish-coalescing.solution.ts
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diff --git a/src/038-unions-and-narrowing/050-intro-to-discriminated-unions.problem.ts b/src/038-unions-and-narrowing/051-intro-to-discriminated-unions.problem.ts
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diff --git a/src/038-unions-and-narrowing/050-intro-to-discriminated-unions.solution.ts b/src/038-unions-and-narrowing/051-intro-to-discriminated-unions.solution.ts
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diff --git a/src/038-unions-and-narrowing/051-destructuring-a-discriminated-union.problem.ts b/src/038-unions-and-narrowing/052-destructuring-a-discriminated-union.problem.ts
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diff --git a/src/038-unions-and-narrowing/052-narrowing-a-discriminated-union-with-a-switch-statement.problem.ts b/src/038-unions-and-narrowing/053-narrowing-a-discriminated-union-with-a-switch-statement.problem.ts
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diff --git a/src/038-unions-and-narrowing/053-narrowing-with-switch-true.explainer.ts b/src/038-unions-and-narrowing/054-narrowing-with-switch-true.explainer.ts
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