UPSC NDA Math Model Paper 8

Given, The distributions X and Y with the total number of observations 36 and 64, and mean 4 and 3 respectively are combined.
4=

X

36

and 3=

Y

64

⇒ X = 144 and Y = 192
⇒ X + Y = 144 + 192
⇒ X + Y = 336
Total number of observations = 36 + 64 = 100
Mean =

sum of observations

total number of observations

⇒ Mean =

336

100

⇒ Mean =3.36