Selecting specific rows and then summing them up

Hi, suppose I have a matrix A=[1 2 3 4 5 6 7 8 9 10 11 13......12555], I want to select specific elements and add them up in one value. Selection is done after uniform interval. For example, I let the first value to be selected in 1 in the first row and then the next value I would select should be in the tenth row which is the value 10, the next value would be in the 20th row and so on. Then sum all these values together and find their mean. Kindly help me figure out how to go about it. Thanks.

Answer 1

[Chunru]

 A=[1:12555];
 B = A(10:10:end);        % choose 10,20,30,...
 mean(B)

ans = 6280

[okoth ochola]

Thanks, it was such helpful

[Stephen23]

A=[1:12555];
% ^       ^  totally superfluous, get rid of them.

[Chunru]

@Stephen23 See the question https://www.mathworks.com/matlabcentral/answers/1761460-or-in-constructing-array