Let the numbers be x,y,z Thus, x:y=5:2 -----------(i) and y;z=5:4-------------(ii) Multiplying equation (i) by 5 and equation (ii) by 2 ⇒ x:y:z=25:10:8 Let x=25k,y=10k and z=8k ⇒ Product = 25k×8k=1800 ⇒ k2=
1800
200
=9 ⇒ k=√9=3 ∴ Sum of three numbers = 25k+10k+8k=43k = 43×3=129