Question

The numbers x1, x2, x3......... x20 are in increasing AP. The sum of the first and last term of these obersvation is 20. The arithmetic mean of the data is _____​

Answer 1

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

Answer 2

Answer:10

Step-by-step explanation: