var students = [['David', 80], ['Vinoth', 77], ['Divya', 88], ['Ishitha', 95], ['Thomas', 68]];  
  
var Avgmarks = 0;  
  
for (var i=0; i < students.length; i++) {  
        Avgmarks += students[i][1];  
        var avg = (Avgmarks/students.length);  
}  
  
alert("Average grade: " + (Avgmarks)/students.length);  
  
        if (avg < 60){  
          console.log("Grade : F");        
          }   
        else if (avg < 70) {  
                console.log("Grade : D");   
                  }   
        else if (avg < 80)   
             {  
                console.log("Grade : C");   
        } else if (avg < 90) {  
                console.log("Grade : B");   
        } else if (avg < 100) {  
                console.log("Grade : A");   
}