Solutions
a)
> marks_matrix(c(20,23,18,48,16,15,18,40,25,20,22,40,14,19,18,42),byrow=T,
+ nrow=4,dimnames=list(NULL,c("Test1","Test2","Test3","Final")))
b)
> marks_rbind(marks,c(10,15,14,30))
> marks
Test1 Test2 Test3 Final
[1,] 20 23 18 48
[2,] 16 15 18 40
[3,] 25 20 22 40
[4,] 14 19 18 42
[5,] 10 15 14 30
c)
> marks[5,2]_17
> marks
Test1 Test2 Test3 Final
[1,] 20 23 18 48
[2,] 16 15 18 40
[3,] 25 20 22 40
d)
> marks[marks[,1]>16,4]
[1] 48 40
e)
> marks[,-3]
Test1 Test2 Final
[1,] 20 23 48
[2,] 16 15 40
[3,] 25 20 40
[4,] 14 19 42
[5,] 10 17 30
f)
> nrow(marks)
[1] 5