An alloy consists of $27\dfrac{1}{2}$ kg of copper and $2\dfrac{3}{4}$ kg of tin. Find the ratio by weight of tin to the alloy.

Find the compounded ratio of:

(i) 2 : 3 and 4 : 9

(ii) 4 : 5, 5 : 7 and 9 : 11

(iii) (a - b) : (a + b), (a + b)² : (a² + b²) and (a⁴ - b⁴) : (a² - b²)²

Find the triplicate ratio of :

(i) 3 : 4

(ii) $\dfrac{1}{2} : \dfrac{1}{3}$

(iii) 1³ : 2³

Find the sub-duplicate ratio of :

(i) 9 : 16

(ii) $\dfrac{1}{4} : \dfrac{1}{9}$

(iii) 9a² : 49b²