Ratio of first and second number =3:4 Ratio of second and third number =5:6 Now, ratio of first, second and third number = =3×5:5×4:4×6 =15x:20x:24x Difference between first and third number is 1125. ⇒24x−15x=1125 ⇒9x=1125 ⇒x=125 So, second number =20×125 and third number =24×125 Average of second and third number =