An adult can drink a bottle of juice in 27 days.
In one day, a man can drink 1/27 of a bottle.
An child can drink a bottle of juice in 54 days.
In one day, a child can drink 1/54 of a bottle.
To solve this, add up their rates:
When you combine them together, 1/27 + 1/54 = 2/54 + 1/54 => 3/54
Simplify the answer: 3/54 => 1/18.
If they both put their efforts into drinking from the same bottle, both an adult and a child can finish 1/18 of a bottle a day. So how many days would it take them to finish one bottle of juice?
1 ÷ 1/18 => 18/18 ÷ 1/18 = 18 days.
It would take them a total of 18 days to finish the bottle of juice.
Just remember, kids: All things in moderation, and don't force yourself to drink a whole bottle at one go.