Question

the average of 9 observation was 9, that of the 1st of 5 being 10 and that if the last 5 being 8. What was the 5th observation

Answer 1

Answer:

if we add 9 numbers =9*9=81

first 5 numbers added to 10*5=50

last 5 numbers added to 8*5=40

If we add last two conditions total is 50+40=90

here all 9 numbers are added and also 5th number once more added

so 5th observation is 90–81=9