diff --git a/src/main/java/com/kpi/fict/DefaultStudentService.java b/src/main/java/com/kpi/fict/DefaultStudentService.java
index 02e85ea..7127805 100644
--- a/src/main/java/com/kpi/fict/DefaultStudentService.java
+++ b/src/main/java/com/kpi/fict/DefaultStudentService.java
@@ -1,9 +1,13 @@
 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.Comparator;
 import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
 
 public class DefaultStudentService implements StudentService {
     private StudentRepository studentRepository;
@@ -14,28 +18,121 @@ public DefaultStudentService(StudentRepository studentRepository) {
 
     @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> 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());
     }
 
+    // c
     //Delimiter: ','
     @Override
     public List<String> getExamSumAndRatingForEachStudent() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository
+                .findAll()
+                .stream()
+                .map(s -> {
+                    Optional<Double> sum = s
+                            .getExams()
+                            .stream()
+                            .map(Exam::getScore)
+                            .reduce(Double::sum);
+                    double _sum = sum.isPresent() ? sum.get() : 0;
+                    return _sum + "," + s.getRating() + "," + s.getName();
+                })
+                .collect(Collectors.toList());
     }
 
     @Override
     public List<Student> findStudentsWhoTakeMathEngExamWith180RatingOrMore() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        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() > 180 &&
+                        s
+                                .getExams()
+                                .stream()
+                                .filter(e -> e.getType() == Exam.Type.ENGLISH)
+                                .findFirst()
+                                .orElse(new Exam(Exam.Type.ENGLISH, 0))
+                                .getScore() > 180
+                )
+                .collect(Collectors.toList());
     }
 
     @Override
     public List<Student> findTwoStudentsWithMaxEngRating() {
-        throw new UnsupportedOperationException("Need to make implementation");
+        return studentRepository
+                .findAll()
+                .stream()
+                .sorted((a, b) -> {
+                    Optional<Exam> aa = a
+                            .getExams()
+                            .stream()
+                            .filter(e -> e.getType() == Exam.Type.ENGLISH)
+                            .findFirst();
+                    Optional<Exam> bb = b
+                            .getExams()
+                            .stream()
+                            .filter(e -> e.getType() == Exam.Type.ENGLISH)
+                            .findFirst();
+                    double _aa = aa.map(Exam::getScore).orElse(0.0);
+                    double _bb = bb.map(Exam::getScore).orElse(0.0);
+                    return Double.compare(_bb, _aa);
+                })
+                .limit(2)
+                .sorted(Comparator.comparing(Student::getName))
+                .collect(Collectors.toList());
     }
 
     public StudentRepository getStudentRepository() {