Arrange the following ratios in descending order of magnitudes :

(i) (5 : 6), (8 : 9), (13 : 18) and (19 : 24)

(ii) (6 : 7), (13 : 14), (19 : 21) and (23 : 28)

(iii) (7 : 12), (9 : 16), (13 : 20) and (5 : 8)

Arrange the following ratios in ascending order of magnitudes :

(i) (4 : 9), (6 : 11), (7 : 13) and (27 : 50)

(ii) (2 : 3), (8 : 15), (11 : 12) and (7 : 16)

(iii) (3 : 5), (4 : 9), (5 : 11) and (10 : 17)

Find x, when :

(i) 3 : 4 :: 2.4 : x

(ii) 1 : 3 :: x : 7

(iii) x : 1.5 :: 3 : 5

Find the fourth proportional to :

(i) 3, 8 and 21

(ii) 1.4, 3.2 and 7

(iii) 1.5, 4.5 and 3.6

(iv) a², ab and b²

(v) (a² − ab + b²), (a³ + b³) and (a − b)