Short Trick:
Given that,
8x + 12x + 15x = 140
⇒ 35x = 140
⇒ x = 4
⇒ The second number = 12 × 4 = 48
∴ The second number is 48.
Detailed Solution : The first number : The second number = (2 : 3) × 4 = 8 : 12
The second number : The third number = (4 : 5) × 3 = 12 : 15
⇒ The first number : The second number : The third number = 8 : 12 : 15
Let the first, second and third number is 8x, 12x and 15x
⇒ 8x + 12x + 15x = 140
⇒ 35x = 140
⇒ x = 4
⇒ The second number = 12 × 4 = 48
∴ The second number is 48.