At a party, every ninth guest gets a cup and every tenth guest gets a mug. What is the position of the first guest that will get both a cup and a mug?
Multiples of 9: 9, 18, 27, 36, 45, 54, 63, 72, 81, 90
Multiples of 10: 10, 20, 30, 40, 50, 60, 70, 80, 90
Position of first guest that gets both a cup and mug
= Lowest common multiple of 9 and 10
= 90
Answer(s): 90