Atrait has two alleles, and their frequencies are represented by p and q. if p = 0.90, what is q?

The sum of the frequency is equal to 1.
 Therefore, we have the following equation:
 p + q = 1
 Substituting values we have:
 0.90 + q = 1
 Clearing the value of q we have:
 q = 1 - 0.90
 q = 0.10
 
 The value of q is given by:
 q = 0.10