Question

thw mean of 20 number is 18 . if 3 is added to each of the first ten numbers , find the mean of the new set of 20 number​

Answer 1

Step-by-step explanation:

mean = sum / no. of no.s

sum = mean × no. of no.s

= 18×20

= 360

when 3 is added to each of first 10 no.s

new sum = 3×10 +360 = 30+360 = 390

new mean = new sum/20 = 390/20 = 19.5

Answer 2

Answer:

19.5

Step-by-step explanation:

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