Given: The average of six numbers = 40 The average of first three numbers = 35 The fifth number is 5 more than the fourth number and sixth number is 10 more than the fourth number Concept: If average of N numbers is x, then total sum of N numbers = Nx Calculation: The average of six numbers = 40 ⇒ Total sum of 6 numbers =6×40=240 The average of first three numbers = 35 ⇒ Total sum of first 3 numbers =3×35=105 ∴ Total sum of 4th,5th, and 6th numbers =240−105=135 Let x be the 4th number, 5th number = x + 5 6th number = x + 10 Now, Total sum of 4th, 5th, and 6th numbers =x+(x+5)+(x+10)=135⇒3x+15=135 ⇒ 3x=120 ∴ x = 40 5th number =x+5=40+5=45