Grid[{{"год.",1900, 1910, 1920, 1930, 1940, 1950, 1960, 1970, 1980, 1990, 2000},{"население (млн.)",1650,1750,1860,2070,2300,2560,3040,3710,4450,5280,6080}},Frame-> All]

info = {{1900,1650},{1910,1750},{1920,1860},{1930,2070},{1940,2300},{1950,2560},{1960,3040},{1970,3710},{1980,4450},{1990,5280},{2000,6080}}

plot = ListPlot[info,PlotStyle->{ Blue},AxesLabel->{"Година","Население в млн."},PlotLegends->{"Данни"},PlotRange->{0,6500}]

f1[x_] =Fit[info,{1,x,x^2},x]

plot1=Plot[f1[x],{x,1900,2000},PlotStyle->{Dashing[0.04],Thick,Black},AxesLabel->{"Година","Население в млн."},PlotRange->{0,6500},PlotLegends->{"Приближение до (x^2)"}]

f2[x_] =Fit[info,{1,x,x^2,x^3},x]

plot2=Plot[f2[x],{x,1900,2000},PlotStyle->Red,AxesLabel->{"Година","Население в млн."},PlotRange->{0,6500},PlotLegends->{"Приближение до (x^3)"}]

plotobstho=Show[plot,plot1,plot2]

Limit[((f2[x+Δx]-f2[x])/(Δx)),Δx->0]

skorostf2[x_] = 12822.979023 -14.122844 x+0.003881 (x^2)

plotskorost=Plot[skorostf2[x],{x,1900,2000},PlotStyle->{Blue,Thick},AxesLabel->{"Година","Скорост на изменение"}]

GraphicsRow[{plotskorost,plotobstho}]

naselenie$1925=f2[1925]