To find the value of x in the equation 5:3 = 11/2 : 3 3/10х, we can first simplify the right side:

11/2 : 3 3/10x = (11/2) / (3 + 3/10x)
= 11/2 / (30/10 + 3/10x)
= 11/2 / (33/10x)
= 11/2 * (10x/33)
= 110x / 66
= 55x / 33
= 5x/3

So now we have the equation 5:3 = 5x/3. By cross multiplying, we get:

3 5 = 5 x
15 = 5x
x = 15/5
x = 3

Therefore, the value of x in the equation is 3.