diff --git a/src/main/java/com/kpi/fict/DefaultStudentService.java b/src/main/java/com/kpi/fict/DefaultStudentService.java
index 1f47f2d..21bfd97 100644
--- a/src/main/java/com/kpi/fict/DefaultStudentService.java
+++ b/src/main/java/com/kpi/fict/DefaultStudentService.java
@@ -1,9 +1,12 @@
 package com.kpi.fict;
 
+import com.kpi.fict.entities.Exam;
 import com.kpi.fict.entities.Student;
 import com.kpi.fict.repositories.StudentRepository;
 
+import java.util.Collection;
 import java.util.List;
+import java.util.stream.Collectors;
 
 public class DefaultStudentService implements StudentService {
     private StudentRepository studentRepository;
@@ -14,28 +17,71 @@ public DefaultStudentService(StudentRepository studentRepository) {
 
     @Override
     public List<Student> findAllWithRatingLessThan300() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository
+                .findAll()
+                .stream()
+                .filter(s -> s
+                        .getExams()
+                        .stream()
+                        .map(Exam::getScore)
+                        .reduce(0.0, Double::sum) < 300)
+                .collect(Collectors.toList());
     }
 
     @Override
     public double findAvgRatingOfMathExam() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository
+                .findAll()
+                .stream()
+                .map(Student::getExams)
+                .flatMap(Collection::stream)
+                .filter(e -> e.getType() == Exam.Type.MATH)
+                .mapToDouble(Exam::getScore)
+                .average()
+                .orElse(0.0);
     }
 
     //Delimiter: ','
     @Override
     public List<String> calculateAvgRatingForEachStudent() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository
+                .findAll()
+                .stream()
+                .map(s -> s.getName() + "," + s
+                        .getExams()
+                        .stream()
+                        .mapToDouble(Exam::getScore)
+                        .average()
+                        .orElse(0.0))
+                .collect(Collectors.toList());
     }
 
     @Override
     public List<Student> findStudentsWithoutExams() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository
+                .findAll()
+                .stream()
+                .filter(s -> s.getExams().size() == 0)
+                .collect(Collectors.toList());
     }
 
     @Override
     public List<Student> findStudentsWithRatingMoreThanAvgAndTakeMathExam() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        double avgRating = studentRepository
+                .findAll()
+                .stream()
+                .mapToDouble(Student::getRating)
+                .average()
+                .orElse(0.0);
+
+        return studentRepository
+                .findAll()
+                .stream()
+                .filter(s -> s.getRating() > avgRating && s
+                        .getExams()
+                        .stream()
+                        .anyMatch(e -> e.getType() == Exam.Type.MATH))
+                .collect(Collectors.toList());
     }
 
     public StudentRepository getStudentRepository() {