The average of a and 2b is 2, and the average of a and 2c is 8. what is the average of a, b, and c

Since we know the average of a and 2b is 2 
⇒ The total of a and 2b is 2 x 3 = 6

Since we know the average of a and 2c is 8 
⇒ The total of a and 2c is 8 x 3 = 24

The total of a  and 2b = 6
The total of a and 2c  = 24
So we total all up:
⇒2a + 2b + 2c = 6 + 24
⇒2a + 2b + 2c = 30            // Combine like terms
⇒ a + b + c = 15                 //Divide by 2 through

The total of a, b and c is 15. Now we can calculate the average of the 3:
Average of a + b + c = 15/3 
Average of a + b + c = 5


The average is 5.