Let the two numbers be 4x and 5x respectively.
The HCF of 4x and 5x is x.
⇒ x = 13
We know that,
Product of two numbers x and y = LCM(x, y) × HCF(x, y)
⇒ 4 × 13 × 5 × 13 = LCM × 13
⇒ LCM = 260