PSLE
Joelle baked some cookies. She gave ¹₈ of the cookies to her friends and 111 to her relatives. She was left with ¹₂ of the cookies. She packed these into 18 boxes. Some boxes contained 7 cookies while the rest contained 9 cookies.

1. How many cookies were packed into the 18 boxes?
2. How many boxes contained 9 cookies?

(a)
Fraction of the cookies given to her relatives
= 1 - ¹₈ - ¹₂

= 1 - ¹₈ - ⁴₈
= ³₈

Number of cookies that Joelle gave to her relatives = 3 u

3 u = 111

1 u = 111 ÷ 3 = 37

Number of cookies that were packed in 18 boxes
= 4 u
= 4 x 37
= 148

Number of cookies that were packed in 18 boxes = 148

Boxes of 9	Cookies	Boxes of 7	Cookies	Total cookies
18	162	0	0	162
17	153	1	7	160

If all the cookies are packed in boxes of 9, the number of cookies needed
= 18 x 9
= 162

Small difference
= 162 - 160
= 2

Big difference
= 162 - 148
= 14

Number of boxes of 7 cookies 
= 14 ÷ 2
= 7

Number of boxes of 9 cookies
= 18 - 7
= 11

Answer(s): (a) 148; (b) 11