Sum of 12 numbers =42×12=504 um of last 5 numbers =5×40=200 um of last 4 numbers =4×44=176 Let 5th number be x then, 6th number will be (x−6) and, 7th number will be (x−1) ∴176+200+x+(x−6)+(x−1)=504 ⇒x=45 ∴ 5th number =45 6th number =39 7th number =44 ∴ Average of 5th&7th number =