Hi Shirley,

Following pls find my worked solution:

A : (B + C + D) -- (1)

3 : 7

B : (A + C + D) -- (2)

5 : 6

C : D -- (3)

2 : 3

Apply <Unchanged Total> concept to (1), (2) since total units in (1) must be the same as (2).

To do this, multiply (1) by 11 , (2) by 10 as follows:

(1) × 11

A : (B + C + D) -- (4)

33 : 77

(2) × 10

B : (A + C + D) -- (5)

50 : 60

From (4), we have ... {the same for (5)}

B + C + D = 77

C + D = 77 - 50 = 27

From (3), C + D = 5. Hence, multiply this ratio by 27, and multiply (4), (5) by 5. These gave the following:

(4) × 5

A : (B + C + D) -- (6)

165 : 385

(5) × 5

B : (A + C + D) -- (7)

250 : 300

(3) × 27

C : D -- (3)

54 : 81

Hence, A = 165; B = 250, C = 54, D = 81

Given A + B + C + D = 6600, we have ...

165u + 250u + 54u + 81u --> 6600

550u --> 6600

1u --> 12

D = 81u --> 81 × 12 = **972**

==================

Trust this helps.

Do let me know again if this is different from your Answerkey or if theres further clarification.

Cheers,

Edward