If the mean of 45 observations is 49. If 3 is added to 10 observations and 5 is subtracted from other 10 observations. Find the new mean.
Very urgent
You are changing the sum by 3*10 - 5*10 = -20
so the mean will change by -20/45
algebraically, the new mean is
(45*49 + 30-50)/45 = 49 - 20/45