Answered

A music store gives every 20th customer a five dollar gift card every 50th customer gets a $10 gift card which customer will be the first to receive both types of gift cards



Answer :

real0unicorn
The 100th just multiply 50 and 0 
texaschic101
lowest common multiple of 20 and 50 is 100....so the 100th customer will be the first to get both types of cards