There are 20 children at a library. six of the children have an average age of 5 years. the remaining children have an average age of 8 years. what is the average age of the children at the library?

So if there are twenty children and 6 have an average age of five, you could say their total age together is 30 years. The others (20-6) have an age of 8.

30+ (20-6)*8 = total age of every child at the library. From there divide by the number of children.

The first one is correct