Percentages and probabilities

Question

A retail shop accepts only cash or checks. Suppose that
% of its customers carry cash,
% carry checks, and
% carry cash or checks (or both). What is the probability that a randomly chosen customer at the shop is carrying both cash and checks?
Write your answer as a decimal (not as a percentage).

Answer 1

 

 S is the percent of customers carrying only cash

 K is the percent of customer carrying only checks

 

 So the probability is 100% - S - K