How to calculate cumulative average of every n values in a matrix?

Hi, I have 300x20 matrix (A). How to calculate average of every 3 consecutive rows of each column to have output matrix B (100x20)?

Answer 1

[Ridwan Alam]

B = (A(1:3:end,:)+A(2:3:end,:)+A(3:3:end,:))/3

Answer 2

[JESUS DAVID ARIZA ROYETH]

solution:

mean100x20=reshape(mean(reshape(A,3,[])),100,[])

Answer 3

[Parthu P]

Thank you both.