diff --git a/src/main/java/com/kpi/fict/DefaultStudentService.java b/src/main/java/com/kpi/fict/DefaultStudentService.java
index 93c681e..926feba 100644
--- a/src/main/java/com/kpi/fict/DefaultStudentService.java
+++ b/src/main/java/com/kpi/fict/DefaultStudentService.java
@@ -1,9 +1,11 @@
 package com.kpi.fict;
 
 import com.kpi.fict.entities.Student;
+import com.kpi.fict.entities.Exam;
 import com.kpi.fict.repositories.StudentRepository;
 
 import java.util.List;
+import java.util.stream.Collectors;
 
 public class DefaultStudentService implements StudentService {
     private StudentRepository studentRepository;
@@ -14,27 +16,62 @@ public DefaultStudentService(StudentRepository studentRepository) {
 
     @Override
     public List<Student> findStudentsWithTwoExams() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository.findAll().stream().filter(student -> student.getExams().size() == 2).collect(Collectors.toList());
     }
 
     @Override
     public List<Student> findStudentsWhoTakeMathAndOneMoreExam() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository.findAll().stream().filter(student -> 
+            student
+                .getExams()
+                .stream()
+                .anyMatch(exam -> exam.getType() == Exam.Type.MATH)
+            && 
+            student
+                .getExams()
+                .size() == 2
+        ).collect(Collectors.toList());
     }
 
     @Override
     public List<Student> findStudentsWithRatingMoreThanAvgAndTakeMathExam() {
-        throw new UnsupportedOperationException("Need to make implementation");
+
+        Double avg = studentRepository.findAll().stream().mapToDouble(Student::getRating).average().orElseThrow(NoSuchFieldError::new);
+        
+        return studentRepository.findAll().stream().filter(student -> 
+            student
+                .getExams()
+                .stream()
+                .anyMatch(exam -> exam.getType() == Exam.Type.MATH)
+            && 
+            student
+                .getRating()
+                > avg
+        ).collect(Collectors.toList());
     }
 
     @Override
     public List<String> getExamSumAndRatingForEachStudent() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository.findAll().stream().map(student -> 
+            String.join(
+                ",",
+                student.getExams().stream().map(exam -> exam.getScore()).reduce(0.0, (a, v) -> a + v).toString(),
+                Double.toString(student.getRating()),
+                student.getName()
+            )
+        ).collect(Collectors.toList());
     }
 
     @Override
     public Student findFirstWithoutMath() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository.findAll().stream().filter(student -> 
+            student
+                .getExams()
+                .stream()
+                .filter(exam -> exam.getType() == Exam.Type.MATH)
+                .findAny()
+                .isEmpty()
+        ).findFirst().orElseThrow(NoSuchFieldError::new);
     }
 
     public StudentRepository getStudentRepository() {