Unit-part method

3 units - 132 cookies = 2 parts ---①


2 units - 92 cookies = 1 part
So 4 units - 184 cookies = 2 parts ---②

Realise that ① and ② are equal.


So,

3 units -132 cookies = 2 units - 184 cookies
1 unit = 52 cookies

1 part = 2 units - 92 cookies
= 2 x 52 - 92
= 104 - 92
= 12 cookies

No. of cookies left in the end
= 3 parts
= 3 x 12 cookies
= 36 cookies

Assumption method

Assume all cookies were sold in packets of 4 first.

36 cookies ÷ 4 cookies per packet
= 9 packets

9 packets x $1 each = $9 earned
However, $11 was earned.

Now, if the cookies in 1 packet were taken out and sold separately at $0.50 each,

Extra amount earned from that 4 cookies
= $0.50 x 4 - $1
= $2 - $1
= $1

$11 - $9 = $2
$2 ÷$1 = 2

This means 2 packets worth of cookies were sold separately at $0.50 each.

2 x 4 = 8

8 cookies were sold at $0.50 each.