Solutions

> x_c(2,6,9,17,39)
> (prod(x))^(1/length(x))
[1] 9.353787

> x_765
> x1_x %/% 100

> x1
[1] 7

> x_x %% 100
> x
[1] 65

> x2_x %/% 10

> x2
[1] 6

> x3_x %% 10

> x3
[1] 5

> quiz_c(24,22,17,10,12,13,16,19,15,18,22,21)
> diff(quiz)
 [1] -2 -5 -7  2  1  3  3 -4  3  4 -1

> A_matrix(c(3,2,6,5,-3,4,6,3,-2),byrow=T,nrow=3)
> A
     [,1] [,2] [,3]
[1,]    3    2    6
[2,]    5   -3    4
[3,]    6    3   -2
> B_c(44,18,14)
> solve(A,B)
[1] 2 4 5

> size
     Weight Waist heights
[1,]    130    26     140
[2,]    110    24     155
[3,]    118    25     142
[4,]    112    25     175
[5,]    128    26     170
> colsum_apply(size,2,sum)
> colsum
 Weight Waist heights
    598   126     782