PSLE
Sarah baked some cookies. She gave ¹₂ of the cookies to her students and 45 to her friends. She was left with ⁷₂₀ of the cookies. She packed these into 15 boxes. Some boxes contained 4 cookies while the rest contained 9 cookies.

1. How many cookies were packed into the 15 boxes?
2. How many boxes contained 9 cookies?

(a)
Fraction of the cookies given to her friends
= 1 - ¹₂ - ⁷₂₀

= 1 - ¹⁰₂₀ - ⁷₂₀
= ³₂₀

Number of cookies that Sarah gave to her friends = 3 u

3 u = 45

1 u = 45 ÷ 3 = 15

Number of cookies that were packed in 15 boxes
= 7 u
= 7 x 15
= 105

Number of cookies that were packed in 15 boxes = 105

Boxes of 9	Cookies	Boxes of 4	Cookies	Total cookies
15	135	0	0	135
14	126	1	4	130

If all the cookies are packed in boxes of 9, the number of cookies needed
= 15 x 9
= 135

Small difference
= 135 - 130
= 5

Big difference
= 135 - 105
= 30

Number of boxes of 4 cookies 
= 30 ÷ 5
= 6

Number of boxes of 9 cookies
= 15 - 6
= 9

Answer(s): (a) 105; (b) 9