Question

Find the mean of 30 numbers given mean of ten of them is 12 and the mean of remaning20 is 9.

Answer 1

mean of ten no:s is 12. If s1 is the sum if these ten numbers, then:

mean of ten numbers= 12
s1/10 = 12
so, s1 = 12*10
s1= 120


mean of remaining twenty no:s is 9. If s2 is the sum if these twenty numbers, then:

mean of twenty numbers= 9
s2/20 = 9
so, s2 = 9*20
s2= 180

Therefore:
mean of the 30 numbers
= sum of the 30 no:s/30
=(s1 + s2) / 30
= (120 + 180) / 30
= 300 / 30
= 10
The answer is 10

Answer 2

Answer:

mean of 30 numbers is 10

Step-by-step explanation:

Mean = (Sum of all the observations/Total number of observations)

According to given data,

Sum of 10 numbers/10 = 12

10×12=120

Sum of 20numbers/20 = 9

20×9=180

Mean of 30 numbers = Sum of 30 numbers/30

120+180/30 = 10

Therefore,

mean of 30 numbers is 10