
data =[...
20250  44250;...
51000 126000;...
77250 100500;...
39000  58500;...
40500  69750;...
42750  76500;...
78750 155250;...
42750  67500];

minutes30 = data(1:4,1)./data(1:4,2)
minutes60 = data(5:8,1)./data(5:8,2)

%minutes30 = 0.4576 0.4048 0.7687 0.6667
%minutes60 = 0.5806 0.5588 0.5072 0.6333

n1 = 4; n2 = 4;
xbar1 = mean(minutes30) %0.5744
xbar2 = mean(minutes60) %0.5700
alpha = 0.05;
s1 = std(minutes30) %0.1719
s2 = std(minutes60) %0.0522

sp = sqrt( ((n1-1)*s1^2 + (n2-1)*s2^2)/(n1 + n2 - 2)) %0.1270
[xbar1-xbar2 - tinv(1-alpha, n1+n2-2)*sp*sqrt(1/n1+1/n2),...
xbar1-xbar2 + tinv(1-alpha, n1+n2-2)*sp*sqrt(1/n1+1/n2)]
% -0.1702    0.1790

tt = (xbar1-xbar2)/(sp*sqrt(1/n1+1/n2))
1-tcdf(tt,  n1+n2-2)