GIVEN: average of 11 observations = 45 average of 12 observations = 44 FORMULA USED: average = sum of observations/total number of observations CALCULATION: sum of 11 observations =45×11=495 sum of 12 observations =44×12=528 12th observation =528−495=33 new observation = old average - (difference in average × total observations) 12th observation =45−(1×12)=33