Question

the mean of first 25 observation is 65 and the mean of next 10 observations is 62.Find the mean of all 35 observations ​

Answer 1

$sum \: 1st \: 25 \: obs. = 65 \times 25 = 1625 \\ \\ sum \: 2nd \: 10 \: obs. = 10 \times 62 = 620 \\ \\ mean = \frac{1625 + 620}{35} \\ \\ = \frac{2245}{35} \\ \\ = 64.14$

Answer 2

Mean of 25 observations = 65 ...means sum of all observations = 25*65 = 1625

Mean of next 10 observation = 62 means ...further sum = 10*62 = 620

Now to find the mean of total 25+10 observations we simply add both the sums and divide by 35.

(1625 + 620)/35 = 64.1428