Answer:
Carl and Antonia see other after every 21 days or after every three weeks.
Step-by-step explanation:
i) Carl goes to the beach every third day.
ii) Antonia goes to the beach every seventh day.
iii) the lowest common multiple of 3 and 7 is LCM(3,7) = 3 [tex]\times[/tex] 7 = 21
iv) therefore Carl and Antonia see other after every 21 days or after every three weeks.
