diff --git a/kangrae-jo/Prefix Sum/10-kangrae-jo.cpp b/kangrae-jo/PrefixSum/10-kangrae-jo.cpp
similarity index 100%
rename from kangrae-jo/Prefix Sum/10-kangrae-jo.cpp
rename to kangrae-jo/PrefixSum/10-kangrae-jo.cpp
diff --git a/kangrae-jo/Prefix Sum/22-kangrae-jo.cpp b/kangrae-jo/PrefixSum/22-kangrae-jo.cpp
similarity index 100%
rename from kangrae-jo/Prefix Sum/22-kangrae-jo.cpp
rename to kangrae-jo/PrefixSum/22-kangrae-jo.cpp
diff --git a/kangrae-jo/PrefixSum/31-kangrae-jo.cpp b/kangrae-jo/PrefixSum/31-kangrae-jo.cpp
new file mode 100644
index 0000000..9dc85e0
--- /dev/null
+++ b/kangrae-jo/PrefixSum/31-kangrae-jo.cpp
@@ -0,0 +1,73 @@
+#include <algorithm>
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+int T, N, M;
+vector<int> A, B;
+
+void input(int& n, vector<int>& v) {
+    cin >> n;
+    v.assign(n, 0);
+    for (int i = 0; i < n; i++) {
+        cin >> v[i];
+    }
+}
+
+vector<int> makeSub(int n, vector<int> v) {
+    vector<int> sub;
+    for (int i = 0; i < n; i++) {
+        int sum = 0;
+        for (int j = i; j < n; j++) {
+            sum += v[j];
+            sub.push_back(sum);
+        }
+    }
+    return sub;
+}
+
+int main() {
+    ios_base::sync_with_stdio(0);
+    cin.tie(0);
+
+    // 0) input
+    cin >> T;
+    input(N, A);
+    input(M, B);
+
+    // 1) A, B 모든 부분합
+    vector<int> subA = makeSub(N, A);
+    vector<int> subB = makeSub(M, B);
+
+    // 2) 정렬
+    sort(subA.begin(), subA.end());
+    sort(subB.begin(), subB.end());
+
+    // 3) 투포인터로 합이 T인 쌍 세기
+    long long answer = 0;
+    int left = 0, right = subB.size() - 1;
+    while (left < subA.size() && 0 <= right) {
+        int sum = subA[left] + subB[right];
+        if (sum == T) {
+            long long countA = 1, countB = 1;
+            while (left + 1 < subA.size() && subA[left] == subA[left + 1]) {
+                countA++;
+                left++;
+            }
+            while (right - 1 >= 0 && subB[right] == subB[right - 1]) {
+                countB++;
+                right--;
+            }
+            answer += countA * countB;
+            left++;
+            right--;
+        } 
+        else if (sum < T) left++;
+        else right--;
+    }
+
+    cout << answer << '\n';
+    
+    return 0;
+}
\ No newline at end of file
diff --git a/kangrae-jo/README.md b/kangrae-jo/README.md
index f72b626..d9a3e9c 100644
--- a/kangrae-jo/README.md
+++ b/kangrae-jo/README.md
@@ -31,4 +31,5 @@
 | 27차시 | 2024.06.01 |  DFS  | [개미굴](https://www.acmicpc.net/problem/14725)|[#107](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/107)|
 | 28차시 | 2024.06.10 |  BFS  | [경주로 건설](https://school.programmers.co.kr/learn/courses/30/lessons/67259)|[#110](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/110)|
 | 29차시 | 2024.06.19 |  TRIE  | [[3차] 자동완성](https://school.programmers.co.kr/learn/courses/30/lessons/17685)|[#114](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/114)|
-| 30차시 | 2024.07.18 |  BFS  | [치즈](https://www.acmicpc.net/problem/2638)|[#117](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/117)|
\ No newline at end of file
+| 30차시 | 2024.07.18 |  BFS  | [치즈](https://www.acmicpc.net/problem/2638)|[#117](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/117)|
+| 31차시 | 2024.07.31 |  Prefix Sum  | [두 배열의 합](https://www.acmicpc.net/problem/2143)|[#122](https://github.com/AlgoLeadMe/AlgoLeadMe-12/pull/122)|
\ No newline at end of file