Gary has guitar lessons every 5 days and band practice every 4 days his first band practice is in 4 days and his first guitar lessons and band practice on the same day explain how you know

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.

Step-by-step explanation:

5-4=1

1+4=5