If A : B = 4 : 5, B: C = 7 : 9 and C : D = 3 : 4, and if A’s share is Tk. 1680, the share of D is -

A : B = 4 : 5;

B : C = 7 : 9
= (7 × 5/7) : (9 × 5/7)
= 5 : 45/7

C : D = 3 : 4
= (3 × 15/7) : (4 × 15/7)
= 45/7 : 60/7.

A : B : C : D
= 4 : 5 : 45/7 : 60/7
= 28 : 35 : 45 : 60.

Let the shares of A, B, C, D be 28x, 35x, 45x, 60x respectively.

Then,
28x = 1680
⇒ x = 1680/28
= 60

∴ D's Share = 60x = Tk. (60 × 60)
= Tk. 3600.