Question

answer 8 no. average question

Answer 1

average of all no. is 30 then the sum of all no. is 180 [30 *6]
average of first four no. is 25 then the sum of first four no. will be 100 [25*4]
 the sum of last two no. =sum of all no. -- sum of first four no. 
                                          = 180-100=80
average of last three no. is 35 then sum of last three no. is 105 [35*3]
fourth no. will be =sum of last three no. - sum of last two no.
                              = 105- 80=25
therefore fourth no. is 25.

Answer 2

average of 6 no. is 30
then
sum of 6 no. = 6*30 =180

average of first 4 no. = 4*25= 100
last 2 no. = (sum of 6 no.) - (sum of 4 no.)
=180 - 100
= 80
average of last 3 no. is 35
then
sum of the last 3 no. = 3*35 = 105
then
4th no. = (sum of last 3 no.) - (sum of last 2 no.)
= 105 - 80
= 25
Hence, 4th no. is 25