Let the ages of the three brothers be x years, y years and z years. x+y=4....(1) y+z=6....(2) z+x=8....(3) Adding (1), (2) and (3), we have 2(x+y+z)=18 ⇒x+y+z=9...(4) From (1) and (4), we have 4+z=9 ⇒z=5 Similarly, y = 1 and x = 3Therefore, age difference between the eldest and the youngest = 5 – 1 = 4 years Trick : Students are advised to think3 numbers such that the sums of two of them at a time are 4 years, 6 years and 8 years. Such numbers are 1, 3 and 5