Solution

Let 

$A_i$ denote that style is selected by $i^{th}$ customer.

Given: $P(A_i)= 0.5, ~~ \forall i \in \{ 1,2,3,4\}.$

Using rule of complements, $P(A_i^c)= 1-P(A_i)= 0.5, ~~ \forall i \in \{ 1,2,3,4\}.$

Answer

0.125