The mean of 8 observations is 12. If one observation of value 20 is replaced by 4, what is the new mean?

हल

1. 01

   The eight observations currently total $8 \times 12 = 96$.

2. 02

   Replacing 20 by 4 reduces the total by 16, giving $96 - 16 = 80$.

3. 03

   The count has not changed, so the new mean is $80 \div 8 = 10$.