If $$x^3y:xy :: xy :a$$​, then which of the options below gives the value of a ?

Correct option is C

Given:

​$$x^3y:xy :: xy :a$$​

Formula Used:

If 4 numbers a, b, c and d are in proportional then:

a : b : :c : d and $$a \times d = b \times c$$​

​$$d = \frac{b\times c}{a}$$​​

Solution:

​$$x^3y:xy :: xy :a$$​

​$$a = \frac{xy\times xy}{x^3y}$$​ 

​$$= \frac{y}{x}$$​​