diff --git a/src/main/java/com/kpi/fict/DefaultStudentService.java b/src/main/java/com/kpi/fict/DefaultStudentService.java
index a59a60e..2a3c0ea 100644
--- a/src/main/java/com/kpi/fict/DefaultStudentService.java
+++ b/src/main/java/com/kpi/fict/DefaultStudentService.java
@@ -6,42 +6,108 @@
 import java.util.List;
 
 public class DefaultStudentService implements StudentService {
-    private StudentRepository studentRepository;
-
-    public DefaultStudentService(StudentRepository studentRepository) {
-        this.studentRepository = studentRepository;
-    }
-
-    @Override
-    public Student findFirstWithoutMath() {
-        throw new UnsupportedOperationException("Need to make implementation");
-    }
-
-    @Override
-    public List<Student> findStudentsWithMathRatingMoreThanAvgAndTakeEngExam() {
-        throw new UnsupportedOperationException("Need to make implementation");
-    }
-
-    @Override
-    public List<String> getExamSumAndRatingForEachStudent() {
-        throw new UnsupportedOperationException("Need to make implementation");
-    }
-
-    @Override
-    public List<Student> findStudentsWithTwoExams() {
-        throw new UnsupportedOperationException("Need to make implementation");
-    }
-
-    @Override
-    public Student findStudentWithMaxEngRating() {
-        throw new UnsupportedOperationException("Need to make implementation");
-    }
-
-    public StudentRepository getStudentRepository() {
-        return studentRepository;
-    }
-
-    public void setStudentRepository(StudentRepository studentRepository) {
-        this.studentRepository = studentRepository;
-    }
+  private StudentRepository studentRepository;
+
+  public DefaultStudentService(StudentRepository studentRepository) {
+    this.studentRepository = studentRepository;
+  }
+
+  @Override
+  public Student findFirstWithoutMath() {
+    return studentRepository
+        .findAll()
+        .stream()
+        .filter(student -> student
+            .getExams()
+            .stream()
+            .noneMatch(exam -> exam.getType() == Exam.Type.MATH))
+        .findFirst()
+        .orElseThrow(NoSuchFieldError::new);
+  }
+
+  @Override
+  public List<Student> findStudentsWithMathRatingMoreThanAvgAndTakeEngExam() {
+    OptionalDouble average = studentRepository
+        .findAll()
+        .stream()
+        .map(Student::getExams)
+        .flatMap(Collection::stream)
+        .filter(exam -> exam.getType() == Exam.Type.MATH)
+        .mapToDouble(Exam::getScore)
+        .average();
+
+    double avg = average.orElseThrow(NoSuchFieldError::new);
+
+    return studentRepository.findAll()
+        .stream()
+        .filter(student ->
+            student.getExams()
+                   .stream()
+                   .anyMatch(exam -> exam.getType() == Exam.Type.ENGLISH)
+            &&
+            student.getExams()
+                   .stream()
+                   .anyMatch(exam -> exam.getType() == Exam.Type.MATH
+            &&
+            exam.getScore() > avg))
+        .collect(Collectors.toList());
+  }
+
+  @Override
+  public List<String> getExamSumAndRatingForEachStudent() {
+        return studentRepository
+              .findAll()
+              .stream()
+              .map(student -> student
+                      .getExams()
+                      .stream()
+                      .mapToDouble(Exam::getScore)
+                      .sum()
+                      + ","
+                      + student.getRating()
+                      + ","
+                      + student.getName())
+              .collect(Collectors.toList());
+  }
+
+  @Override
+  public List<Student> findStudentsWithTwoExams() {
+    return studentRepository
+        .findAll()
+        .stream()
+        .filter(student -> student.getExams().size() == 2)
+        .collect(Collectors.toList());
+  }
+
+  @Override
+  public Student findStudentWithMaxEngRating() {
+    return studentRepository
+        .findAll()
+        .stream()
+        .filter(student -> student
+            .getExams()
+            .stream()
+            .anyMatch(exam -> exam.getType() == Exam.Type.ENGLISH))
+        .max((student, t1) -> {
+          Optional<Exam> score1 = student
+              .getExams()
+              .stream()
+              .filter(exam -> exam.getType() == Exam.Type.ENGLISH)
+              .findFirst();
+          Optional<Exam> score2 = t1
+              .getExams()
+              .stream()
+              .filter(exam -> exam.getType() == Exam.Type.ENGLISH)
+              .findFirst();
+          return (int) (score1.get().getScore() - score2.get().getScore());
+        }).orElseThrow(NoSuchElementException::new);
+  }
+
+  public StudentRepository getStudentRepository() {
+    return studentRepository;
+  }
+
+  public void setStudentRepository(StudentRepository studentRepository) {
+    this.studentRepository = studentRepository;
+  }
 }