A can do work in 12 days and B can do in 15 days the together work complete in how many days

The best way to solve time and work questions is buy considering LCM of the two numbers here u can take 60 as it is divisible by both 12 and 15
If a takes 12 days to complete 60 work it's power is 5 similarly for b 60/15 means it's power is 4
Now when they are working together their total power is 9 and the work to be down is 60 hence the time becomes 60/9

60/9