Answer:
20 days
Step-by-step explanation:
Gary has guitar lessons every 5 days
Gary band practice every 4 days
Gary first guitar lessons and band practice on the same day.
Next day when both practice on same day should be multiple of 4 and 5.
Least common multiple of 4 and 5 ,
4 = 4, 8, 12, 16, 20, 24, ......
5 = 5, 10, 15, 20, 25, ..........
Common multiple in both number is 20.
After 20 days he will got for guitar lesson and band practice same day.
