15.
Work:
O’Leary|| 5, 10, 15, 20, 25, 30, 35, 40, 45, 50
Jones|| 6, 12, 18, 24, 30, 36, 42, 48, 54
The LCM is 30, so in 30 days they will go shopping together again.
16.
Work:
Hot Dogs|| 8, 16, 24, 32, 40, 48, 56, 64, 72, 80
Hot Dogs w/ buns|| 10, 20, 30, 40, 50, 60, 70
The least number of hot dogs with a bun that Riley can make without having any supplies left over is 40.