Average and total problem
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1. What is the average of 10 and 20 ?

2. If the average of a and b is 12, what is their sum ?

3. If the average of a and b is 10, and the average of c and d is 20.
   What is the average of a,b,c,and d ?

4. If a=80, b=70, c=90, and the average of a,b,c, and d is 85.
   What is the value of d ?

5. If the average of a and b is 85. And a=80, what is the value of b ?

6. If the average of a,b,and c is 80. What is the average of a,b,c, 
   and d if the value of d is 92 ?

7. If the average of a and b is 80. What is the average of 
   (a+20) and (b+20) ?

8. If the average of a and b is 80. What i sthe average of
   (a+100) and (b-100) ?

9. If the average of a and b is 70, the average of b and c is 80,
   and the average of a and c is 85. What is the value of a, b, and c ?

10. If 3 integers a,b, and c are in the arithmetic series and their average is 0.
    What is the value of the middle number b ?