Q6

3 donuts for $2

Note that 120 donuts mean 40 groups of 3 donuts, so the total price Mdm Tan paid
= 40 groups of 3 donuts
= 40 x $2
= $80

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6 donuts for $5

Note that 120 donuts mean 20 groups of 6 donuts, so the total price Mr Ang paid
= 20 groups of 6 donuts
= 20 x $5
= $100

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Difference in amount paid
= $100 - $80
= $20

Q7

I am using text to type so I am unable to draw models.

(I attempt to use ▲ for models)

Originally, Minah baked "some muffins". At the end, Minah had 1/4 of the muffins left.

Your model might look like this.

Before: ▲ ▲ ▲ ▲
After: ▲

Am I right to say the above?

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At the end, Minah had ▲ muffins left. This was after she gave 2/3 of the "remaining" muffins left.

So, 1/3 of the "remaining" muffins would be what is left at the end, which we now know is ▲.

This means that the 2/3 of the "remaining" muffins can be represented by ▲ ▲, since 2/3 is twice of 1/3.

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So, before Minah gave 2/3 of the remaining muffins, Minah had ▲ ▲ ▲ muffins,

To recap, here's the breakdown.

▲ ▲ ▲ ▲ at first
▲ ▲ ▲ after selling 252 muffins
▲ after giving away 2/3 of the "remaining muffins" to her mother

Check that ▲ is 1/4 of ▲ ▲ ▲ ▲.

This means that she sold ▲ muffins. So,▲ = 252 muffins.

She gave ▲ ▲ to her mother, or 252 x 2 = 504 muffins.