Answer:
The 60th customer will get both a free coke and a free popcorn.
Explanation:
i) every 10 customer gets a free coke
ii) every 12 customer gets a free popcorn
iii) therefore the first customer who will get both a free coke and a free popcorn will be given by the Lowest Common Multiple of 10 and 12 which is 60, as 10 goes in to 60 by 6 times and 12 goes into 60 by 5 times.