diff --git a/.gitignore b/.gitignore
index 6fbd7ef68d0a0d5dbfeda7ae10e7853d52b9a42e..e8496bd94be7abe3aa4ae9342ceb7cbbe4b4d521 100644
--- a/.gitignore
+++ b/.gitignore
@@ -193,3 +193,5 @@ sympy-plots-for-*.tex/
notebooks/*.ipynb_checkpoints
notebooks/*dataxy
notebooks/*gnuxy
+src/*dataxy
+src/*gnuxy
diff --git a/src/solutions/04_newton.f90 b/src/solutions/04_newton.f90
new file mode 100644
index 0000000000000000000000000000000000000000..f35201696ad59b9caf40d5b8456d3d452daee5de
--- /dev/null
+++ b/src/solutions/04_newton.f90
@@ -0,0 +1,54 @@
+program newton
+
+ implicit none
+
+! Use a Newton iteration to solve the equation
+!
+! x - current approximation to the solution
+! f(x) - polynomial function
+! df - derivative of f with respect to x
+! xo - previous guess for solution
+! eps - convergence criterion
+! dx - change in solution approximation
+! it - number of iterations
+! itmax - maximum number of iterations
+
+ integer, parameter :: itmax = 1000
+ real(8), parameter :: eps = 1.e-6
+
+ integer :: it
+ real(8) :: x,f,df,xo
+
+ it = 0
+ f = 1d0
+
+ write(*,*) 'Try to solve "x**3+x-10=0"'
+ write(*,*) 'What is your initial guess for the solution?'
+ read(*,*) x
+
+ do while( dabs(f)>eps .and. it<=itmax )
+ it=it+1
+ xo=x
+ call derivate(xo,f,df)
+ x = xo -f/df
+ write(*,*) 'it = ',it,', x = ',x,', f(x) = ',f
+ end do
+
+end program
+
+! ******************************************************************************************
+
+subroutine derivate(x,f,d)
+
+! Evaluate the function f(x)=x**3+x-10
+! also return the derivative of the function
+
+ implicit none
+
+ real(8), intent(in) :: x
+ real(8), intent(out) :: f, d
+
+ d = 3*x**2 + 1d0
+ f = x**3 + x - 10d0
+
+end subroutine
diff --git a/src/solutions/04_plot.f90 b/src/solutions/04_plot.f90
new file mode 100644
index 0000000000000000000000000000000000000000..0cacebd26796a3eb1427b37c57ea93f081ea9952
--- /dev/null
+++ b/src/solutions/04_plot.f90
@@ -0,0 +1,50 @@
+program plot
+
+ implicit none
+
+ real(4) :: fx, x
+ integer :: i
+
+ open (112,file='04_gnuxy')
+
+ write(112,*) 'set grid'
+ write(112,*) 'set xzeroaxis'
+ write(112,*) 'set yzeroaxis'
+ write(112,*) 'set border 0 # remove frame'
+ write(112,*) 'set xtics axis # place tics on axis rather than on border'
+ write(112,*) 'set ytics axis'
+ write(112,*) 'set ticscale 0 # [optional] labels only, no tics'
+ write(112,*) 'set xtics add ("" 0) # suppress origin label that lies on top of axis'
+ write(112,*) 'set ytics add ("" 0) # suppress origin label that lies on top of axis'
+ write(112,*) ''
+ write(112,*) '# if arrows are wanted only in the positive direction'
+ write(112,*) 'set arrow 1 from 0,0 to graph 1, first 0 filled head'
+ write(112,*) 'set arrow 2 from 0,0 to first 0, graph 1 filled head'
+ write(112,*) ''
+ write(112,*) '# if arrows in both directions from the origin are wanted'
+ write(112,*) 'set arrow 3 from 0,0 to graph 0, first 0 filled head'
+ write(112,*) 'set arrow 4 from 0,0 to first 0, graph 0 filled head'
+ write(112,*) ''
+ write(112,*) 'set nokey'
+ write(112,*) 'set xrange [-4:4]'
+ write(112,*) 'plot "04_dataxy_1" using 1:2 with lines lt rgb "blue"'
+ write(112,*) 'pause -1'
+
+ close(112)
+
+ ! Generate x-y pairs for the graph
+
+ open (112,file='04_dataxy_1')
+ do i=-40,40
+ x = .1*i
+ fx = x**3+x-10.0
+ write(112,*) x, fx
+ end do
+ close(112)
+
+ print *, ' Hit the Return (Enter) key to continue'
+
+ call system ('gnuplot 04_gnuxy')
+ stop
+
+end
diff --git a/src/solutions/09_ChristmasTree.f90 b/src/solutions/09_ChristmasTree.f90
new file mode 100644
index 0000000000000000000000000000000000000000..e6ec7a26417d86ec322d27a2b888b10de666776d
--- /dev/null
+++ b/src/solutions/09_ChristmasTree.f90
@@ -0,0 +1,34 @@
+program ChristmasTree
+
+ implicit none
+
+ integer i, h, hmax, line, ball
+ character(8) hmax_string
+ character(1) sball
+
+ ! get the command line argument
+ call getarg(1,hmax_string)
+
+ ! cast string to integer
+ read(hmax_string,*) hmax
+
+ ball=1
+ do h=1,hmax
+ line=1
+ ! write spaces to align the head of the tree
+ write(*,'(a)',advance='no') repeat(' ',hmax-h)
+ ! loop to decide when we have to create a new line
+ do while(line.le.(2*h-1))
+ ! modulo to decide when we have to put a ball or not
+ sball='#'
+ if(mod(ball,6).eq.0) sball='o'
+ write(*,'(A)',advance='no') sball
+ ! increment ball/line decision variables
+ ball=ball+1
+ line=line+1
+ enddo
+ ! create a new line
+ write(*,*)
+ enddo
+
+end program
diff --git a/src/solutions/10_eqdiff.f90 b/src/solutions/10_eqdiff.f90
new file mode 100644
index 0000000000000000000000000000000000000000..d054a72a5df88e64f4fac996d8c62d78d434d5a8
--- /dev/null
+++ b/src/solutions/10_eqdiff.f90
@@ -0,0 +1,81 @@
+program eqdiff
+
+ implicit none
+
+ integer, parameter :: nt = 200
+ integer, parameter :: st = 1
+
+ integer :: n
+ real(8) :: pi, A, delta
+
+ real(8), dimension(nt+st) :: U, U1, U2, UU
+ real(8), dimension(nt+st) :: E, E1, E2
+
+ open(100,file="10_results.txt")
+
+ pi=2d0*dacos(0)
+ A=1d0
+ delta=pi/50d0
+
+ U(:)=0d0
+ E(:)=0d0
+ U1(:)=0d0
+ E1(:)=0d0
+ U2(:)=0d0
+ E2(:)=0d0
+ UU(:)=0d0
+
+ write(*,*) "Starting the loop..."
+ write(100,6000) st,U(1),U1(1),U2(1),UU(1),E(1),E1(1),E2(1)
+
+ do n=st,nt
+ U(n+1)=U(n)+delta*A*dcos(n*delta)
+ U1(n+1)=U1(n)+delta*A*dcos((n+0.5d0)*delta)
+ U2(n+1)=U2(n)+delta*A*dcos((n+1d0)*delta)
+
+ UU(n+1)=A*dsin(n*delta)
+
+ E(n+1)=dabs(UU(n+1)-U(n+1))
+ E1(n+1)=dabs(UU(n+1)-U1(n+1))
+ E2(n+1)=dabs(UU(n+1)-U2(n+1))
+
+ write(100,6000) (n+1),U(n+1),U1(n+1),U2(n+1),UU(n+1),E(n+1),E1(n+1),E2(n+1)
+ end do
+
+ write(*,5000) "End of the loop: (",nt,") iterations!"
+
+ open (112,file='10_gnuxy')
+
+ write(112,*) "set multiplot layout 2,1 rowsfirst"
+ write(112,*) "set xlabel 'N'"
+ write(112,*) "set xrange [1:201]"
+ write(112,*)
+ write(112,*) "set ylabel 'U'"
+ write(112,*) "set yrange [-1.2:1.2]"
+ write(112,*) "plot '10_results.txt' using 2 title 'U with N' with lines lt rgb 'blue', \"
+ write(112,*) " '10_results.txt' using 3 title 'U with N+0.5' with lines lt rgb 'red', \"
+ write(112,*) " '10_results.txt' using 4 title 'U with N+1' with lines lt rgb 'green', \"
+ write(112,*) " '10_results.txt' using 5 title 'U analytic' with lines lt rgb 'black'"
+ write(112,*)
+ write(112,*) "set ylabel 'E'"
+ write(112,*) "set yrange [-0.05:0.2]"
+ write(112,*) "plot '10_results.txt' using 6 title 'E with N' with lines lt rgb 'blue', \"
+ write(112,*) " '10_results.txt' using 7 title 'E with N+0.5' with lines lt rgb 'red', \"
+ write(112,*) " '10_results.txt' using 8 title 'E with N+1' with lines lt rgb 'green'"
+ write(112,*)
+ write(112,*) "pause -1"
+ write(112,*) "unset multiplot"
+
+ write(*,*) "See 10_results.txt"
+ write(*,*)
+ write(*,*) "Hit the Return (Enter) key to continue"
+
+ close(112)
+ close(100)
+
+ call system('gnuplot 10_gnuxy')
+
+ 5000 format(1X,A,I3,A)
+ 6000 format(1X,I5,7F14.9)
+
+end