Chapter 13 - Counting and Probability - 13.3 Probability - 13.3 Asses Your Understanding - Page 866: 56

$0.91$

We know that $P(\text{an event happens})=1-P(\text{an event doesn't happen}).$ Hence, here (with $9\%=0.09$) we have $P(\text{does not contain shortbread/trefoils})=1-P(\text{contains shortbread/trefoils})\\ P(\text{never spent any money in gambling})=1-0.09\\ P(\text{never spent any money in gambling})=0.91$