Averaging certain rows in a vector

Hi everyone,

I'm a newcomer to MathCAD and am stuck on a problem.

I have a vector V with n number of data and I want reduce it into a new vector V' in which the first row is the average of the values of first 70 rows from the vector V, then the next row in V' is the average of the values of next set of 70 rows in V, and so forth. I've written the problem more clearly bellow:

I'm really not sure how to tackle this, so I'd be thankful for any input.

Thank you in advance!

Tea