A certain weight (in kg) is divided into two parts such that 5 times the first part added to 11 times the second part makes 7 times the whole weight. The ratio of the first part to the second part is :

2 : 1

Let first and second part of the number be x and y, respectively. Then,

5x + 11y = 7 (x + Y)

11y - 7y = 7x - 5x

4y = 2x

x : y = 2 : 1