Question

ten numbers mean is M. if 5 added to each number then the mean becomes 12.5. then the total of original numbers​

Answer 1

Answer:

Let the 20 observations be X1 ,X2 ,X3 ,…., X20

Sum of n observations = mean × no. of observations

Sum of 20 observations = 18 ×20

X1 + X2 +X3 + ….+X20 = 360 ….…(1)

When 3 is added to first 10 numbers, then sum of new observations will be

(X1+3)+(X2+3)+(X3+3)+…+(X9+3)+(X10+3)+X11+…+X20 = (X1+X2+X3+….+X20)+3×10

=360 + 30 …….(from 1)

=390

So , mean of new observations = 390÷20 = 19.5