If a 2 x 7 matrix is multiplied to a 7x5 matrix, and then the result is multiplied to a 5 x 11 matrix, what is the size of the final result

1.
Let A be a m×n matrix, and B be a n×k matrix, 

then A * B is a matrix of size m×k,

2.
in the given problem:

Multiplying a 2 x 7 matrix by a 7x5 matrix, results in a 2x5 matrix,

multiplying this matrix by a 5 x 11 matrix, then results in a 2×11 matrix.

2×11