Hey Shirley,

Following pls find the worked solutions:

C7.

Apply Simultaneous method here...(aka Compare & Replace / Elimination method )

<Before>

C: 2p + 4

P: 5p

<Process>

P gave away 4.

<After>

C: 2p + 4

P: 5p - 4

Ratio C : P = 8 : 13

Hence we have ...

2p + 4 --> 8u --- (1)

5p - 4 --> 13u --- (2)

Given that question is interested in number of sweets at first, we shall eliminate (u).

(1) x13: 26p + 52 --> 104u --- (3)

(2) x8: 40p - 32 --> 104u --- (4)

(4) - (3): 40p - 26p - 32 - 52 --> 0

14p --> 84

1p --> 6

At first, C = 2p + 4 --> (2 x 6) + 4 = 16

P = 5p --> 5 x 6 = 30

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C11.

Apply Cross-Multiply method here ...

<Before>

T : H

3 : 5

<Process>

+60 +20

<After>

5 : 7

(3u + 60) / 5 = (5u + 20) / 7

7 x (3u + 60) = 5 x (5u + 20)

21u + 420 = 25u + 100

25u - 21u --> 420 - 100

4u --> 320

1u --> 80

Number of stickers T had at first = 3u --> 3 x 80 = 240

*Notes: Simultaneous method can also be employed here. Also, the standard <Before> and <After> model concept by drawing can also be used; however, it can be very 'challenging' to some students.

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Trust this helps. Anything else, pls do clarify.

Cheers,

Edward