diff --git a/src/main/java/com/kpi/fict/DefaultStudentService.java b/src/main/java/com/kpi/fict/DefaultStudentService.java
index ad330d6..b37d799 100644
--- a/src/main/java/com/kpi/fict/DefaultStudentService.java
+++ b/src/main/java/com/kpi/fict/DefaultStudentService.java
@@ -1,8 +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.List;
+import java.util.stream.Collectors;
+
+
 import java.util.List;
 
 public class DefaultStudentService implements StudentService {
@@ -14,28 +18,85 @@ public DefaultStudentService(StudentRepository studentRepository) {
 
     @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> findStudentsWithMathRatingMoreThanAvgAndTakeEngExam() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        double avg = studentRepository
+                .findAll()
+                .stream()
+                .flatMap(s -> s.getExams().stream())
+                .filter(e -> e.getType() == Exam.Type.MATH)
+                .mapToDouble(Exam::getScore)
+                .average()
+                .orElse(0.);
+        return studentRepository
+                .findAll()
+                .stream()
+                .filter(s ->
+                        s
+                                .getExams()
+                                .stream()
+                                .filter(e -> e.getType() == Exam.Type.MATH)
+                                .findFirst()
+                                .orElse(new Exam(Exam.Type.MATH, 0))
+                                .getScore() > avg &&
+                                s
+                                        .getExams()
+                                        .stream()
+                                        .anyMatch(e -> e.getType() == Exam.Type.ENGLISH))
+                .collect(Collectors.toList());
     }
 
     //Delimiter: ','
     @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 findStudentWithMaxAvgExamRating() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository
+                .findAll()
+                .stream()
+                .max((a, b) -> {
+                    double r1 = a
+                            .getExams()
+                            .stream()
+                            .mapToDouble(Exam::getScore)
+                            .average()
+                            .orElse(0.);
+                    double r2 = b
+                            .getExams()
+                            .stream()
+                            .mapToDouble(Exam::getScore)
+                            .average()
+                            .orElse(0.);
+                    return Double.compare(r1, r2);
+                })
+                .orElse(studentRepository.findAll().get(0));
     }
 
     @Override
     public List<Student> findStudentsWhoTakeEngExamWith11RatingOrMore() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return this.studentRepository
+                .findAll()
+                .stream()
+                .filter(student -> student.getExams().size() > 0)
+                .filter(student -> student.getRating() >= 11)
+                .collect(Collectors.toList());
     }
 
     public StudentRepository getStudentRepository() {