Answer: After 12 weeks they will both be at the dentists on the same Tuesday
Explanation:
Since we have given that
He goes for a checkup every fourth Tuesday and his friend goes for a check up every third Tuesday.
We need to find the number of weeks they both will be at the dentist on the same Tuesday.
For this we will find "L.C.M. of 4 and 3 " =12
So, After 12 weeks they will both be at the dentists on the same Tuesday.