hi Shirley

Following pls find my worked solutions:

Q1.

Ratio / Proportion of counters given away:

R : B

9 : 7

Apply <work backwards> method, we have ...

<before>

R |---- 180 ----|<----- 9u ----->|

B |<---- 7u ----->|

Given that R = 2B, we have ...

180 + 9u --> 2 × 7u = 14u

14u - 9u --> 180

5u --> 180

1u --> 36

(a)

There were **36** pupils

(b)

Total counters (at first) = 180 + 16u --> 180 + (16 × 36)

= 180 + 576 = **756**

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Q2.

(a)

9 kg mixture = 9 x 15 = **$135**

(b)

Let Grade A coffee powder be 1u per kg

Given that Grade B coffee powder costs $4.50 per kg

less than Grade A coffee powder, we have ...

B = A - 4.50 = 1u - 4.50

Apply <Number x Value> method,

4u + 5(1u - 450) --> 13500

4u + 5u - 2250 --> 13500

9u --> 13500 + 2250 = 15750

1u --> 1750

Cost of 1 kg Grade A = **$17.50**

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Trust the above helps.

Do let me know again if these answers are different from your Answerkey or if there's further clarification.

Cheers,

Edward