If a : b = 2 : 3, b : c = 4 : 5 and c : d = 6 : 7, find a : b : c : d.

Find the compounded ratio of :

(i) (a - b) : (a + b) and (b² + ab) : (a² - ab)

(ii) (x + y) : (x - y), (x² + y²) : (x + y)² and (x² - y²)² : (x⁴ - y⁴)

(iii) (x² - 25) : (x² + 3x - 10); (x² - 4) : (x² + 3x + 2) and (x + 1) : (x² + 2x).

The ratio of the prices of first two fans was 16 : 23. Two years later, when the price of the first fan had risen by 10% and that of the second by ₹ 477, the ratio of their prices became 11 : 20. Find the original prices of the two fans.