Question

the mean of 25 observation is 65 and mean of next 10 observation is 62 find the mean all 35obseration

Answer 1

Since the product of mean and total no. Of observations gives the sum of all the observations..
Therefore answer is ((25*65)+(10*62))/35=

Answer 2

let the 25 observation be X1 , X2, X3,......,X25
Mean of 25 observation = sum of 25 observation/Number of 25 observation.
65= X1+X²+X3+.......X25/25
X1+X2+X3+.....X25= 65× 25
X1 + X2 + X3+ ........+X25= 1625..(1)
again,
Mean of 10 observation = X1+X2+X3+...+ X10/10
62 = X1+X2+X3+....X10/10
X1+X2+X3+....X10= 62× 10
X1+X2+X3+....X10 = 620
Therefore,
mean of 35 observation= 1625+ 620= 2245.