Java 8, 88 70 60 bytes

Uses a lambda to save bytes, performs the calculation and substrings to return the answer.

(v,a)->"**********".substring(Math.max(0,(int)(10-v/70d/a))) 

Here is my class for testing it.

public class DifficultyCalculator{ static interface h{ String f(int v, int a);} static void g(h H){ System.out.print(H.f(163,2));System.out.println("\t**"); System.out.print(H.f(548,22));System.out.println("\t*"); System.out.print(H.f(1452,24));System.out.println("\t*"); System.out.print(H.f(1713,37));System.out.println("\t*"); System.out.print(H.f(4162,32));System.out.println("\t**"); System.out.print(H.f(3067,15));System.out.println("\t***"); System.out.print(H.f(22421,19));System.out.println("\t**********"); } public static void main(String[] args) { g( // 70 (v,a)->"**********".substring(java.lang.Math.max(0,(int)(10-v/70d/a))) ); } } 

Update

• -10 [16-08-18] Removed unnecessary import, thanks to @OlivierGrégoire!
• -18 [16-08-17] Return string instead of print

Java 8, 57 bytes

Uses a lambda to save bytes, performs the calculation and substrings to return the answer.

(v,a)->"**********".substring(Math.max(0,(700*a-v)/70/a)) 

Here is my class for testing it.

public class DifficultyCalculator{ static interface h{ String f(int v, int a);} static void g(h H){ System.out.print(H.f(163,2));System.out.println("\t**"); System.out.print(H.f(548,22));System.out.println("\t*"); System.out.print(H.f(1452,24));System.out.println("\t*"); System.out.print(H.f(1713,37));System.out.println("\t*"); System.out.print(H.f(4162,32));System.out.println("\t**"); System.out.print(H.f(3067,15));System.out.println("\t***"); System.out.print(H.f(22421,19));System.out.println("\t**********"); } public static void main(String[] args) { g( // 70 (v,a)->"**********".substring(java.lang.Math.max(0,(int)(10-v/70d/a))) ); } } 

Update

• -3 [16-08-19] Utilized integer division
• -10 [16-08-18] Removed unnecessary import, thanks to @OlivierGrégoire!
• -18 [16-08-17] Return string instead of print

Java 8, 88 70 bytes

Uses a lambda to save bytes, performs the calculation and substrings to return the answer.

(v,a)->"**********".substring(java.lang.Math.max(0,(int)(10-v/70d/a))) 

Here is my class for testing it.

public class DifficultyCalculator{ static interface h{ String f(int v, int a);} static void g(h H){ System.out.print(H.f(163,2));System.out.println("\t**"); System.out.print(H.f(548,22));System.out.println("\t*"); System.out.print(H.f(1452,24));System.out.println("\t*"); System.out.print(H.f(1713,37));System.out.println("\t*"); System.out.print(H.f(4162,32));System.out.println("\t**"); System.out.print(H.f(3067,15));System.out.println("\t***"); System.out.print(H.f(22421,19));System.out.println("\t**********"); } public static void main(String[] args) { g( // 70 (v,a)->"**********".substring(java.lang.Math.max(0,(int)(10-v/70d/a))) ); } } 

Update

• -18 [16-08-17] Return string instead of print

Java 8, 88 70 60 bytes

Uses a lambda to save bytes, performs the calculation and substrings to return the answer.

(v,a)->"**********".substring(Math.max(0,(int)(10-v/70d/a))) 

Here is my class for testing it.

public class DifficultyCalculator{ static interface h{ String f(int v, int a);} static void g(h H){ System.out.print(H.f(163,2));System.out.println("\t**"); System.out.print(H.f(548,22));System.out.println("\t*"); System.out.print(H.f(1452,24));System.out.println("\t*"); System.out.print(H.f(1713,37));System.out.println("\t*"); System.out.print(H.f(4162,32));System.out.println("\t**"); System.out.print(H.f(3067,15));System.out.println("\t***"); System.out.print(H.f(22421,19));System.out.println("\t**********"); } public static void main(String[] args) { g( // 70 (v,a)->"**********".substring(java.lang.Math.max(0,(int)(10-v/70d/a))) ); } } 

Update

• -10 [16-08-18] Removed unnecessary import, thanks to @OlivierGrégoire!
• -18 [16-08-17] Return string instead of print

Java 8, 88 bytes

Uses a lambda to save bytes and substrings the 10 asterisk string.

(v,a)->System.out.print("**********".substring(java.lang.Math.max(0,10-(int)(v/70d/a)))) 

Here is my class for testing it.

public class DifficultyCalculator{ static interface h{ void f(int v, int a);} static void g(h H){ H.f(163,2);System.out.println("\t**"); H.f(548,22);System.out.println("\t*"); H.f(1452,24);System.out.println("\t*"); H.f(1713,37);System.out.println("\t*"); H.f(4162,32);System.out.println("\t**"); H.f(3967,15);System.out.println("\t***"); H.f(22421,19);System.out.println("\t**********"); } public static void main(String[] args) { g( // 88 (v,a)->System.out.print("**********".substring(java.lang.Math.max(0,10-(int)(v/70d/a)))) ); } } 

Java 8, 88 70 bytes

Uses a lambda to save bytes, performs the calculation and substrings to return the answer.

(v,a)->"**********".substring(java.lang.Math.max(0,(int)(10-v/70d/a))) 

Here is my class for testing it.

public class DifficultyCalculator{ static interface h{ String f(int v, int a);} static void g(h H){ System.out.print(H.f(163,2));System.out.println("\t**"); System.out.print(H.f(548,22));System.out.println("\t*"); System.out.print(H.f(1452,24));System.out.println("\t*"); System.out.print(H.f(1713,37));System.out.println("\t*"); System.out.print(H.f(4162,32));System.out.println("\t**"); System.out.print(H.f(3067,15));System.out.println("\t***"); System.out.print(H.f(22421,19));System.out.println("\t**********"); } public static void main(String[] args) { g( // 70 (v,a)->"**********".substring(java.lang.Math.max(0,(int)(10-v/70d/a))) ); } } 

Update

• -18 [16-08-17] Return string instead of print