Hi there,

Following pls find my worked solution:

Apply <Unchanged Difference> concept (i.e. difference in savings at the end is the same as before), we have ...

<Before>

T : D Diff

7 : 8 1

<After>

T : D Diff

11 : 14 3

Since the difference is the same, we multiply <Before> ratio 3x ...

<Before>

T : D Diff

21 : 24 3

Comparing the <Before> and <after> ratios, there is a similar decrease of 10u for T and D. Hence,

10u --> 20

1u --> 2

D (savings at first) = 24u --> 24 × 2 = **$48**

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Trust this helps.

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

Cheers,

Edward