Question

find the average of 12 number if first 8numbers average is 21 find the average of last 4 numbers

Answer 1

question is wrong. average of last 4 numbers should be given. It would be 18. If not correct yourself.

average of 8 numbers = 21

sum of 8 numbers = 21 x 8 = 168

Average of last 4 numbers = 18

sum of last 4 numbers = 18 x 4 = 72

So sum of 12 numbers = 168 + 72 = 240

Average of 12 numbers = 240/12 = 20