LCM Word problem Lars, Rita and Alan

This is a GCSE question, around level C / B, that deals with a 'real life' lowest common multiple (LCM) question.

"Lars, Rita and Alan regularly go swimming. Lars goes every 2 days, Rita goes every 3 days and Alan goes every 5 days. They all went swimming on 1st June.
a) On what date will Lars and Rita next go swimming together?
b) On what date will Rita and Alan next go swimming together?
c) On what day of the week will all 3 next go swimming together?
d) Which of the three (if any) will go swimming on 15th June?

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