How to reassign matrix if it is greater than some value quickly

Considering a Matrix

a =   [ 11 20  51  23  100 3
      2  25  15  12 80  8
      1  15  20  50 22  8
      6  1   23  12 50  6 ]

Is there any function that could quickly reassign matrix to specific value if it is less than a value? such as b=10, if it is less than b, reassign it to 0, and having the answer like this:

ans   = [ 11 20  51  23  100 0
        0  25  15  12 80  0
        0  15  20  50 22  0
        0  0   23  12 50  0 ]

Answer 1

[Roger Stafford]

   M = a;
   M(M<b) = 0;

M is your answer.

Answer 2

[Jan]

Or:

b = a .* (a >= 10);