PSLE
Julie baked some cookies. She gave ²₅ of the cookies to her students and 140 to her colleagues. She was left with ¹₄ of the cookies. She packed these into 12 boxes. Some boxes contained 7 cookies while the rest contained 9 cookies.

1. How many cookies were packed into the 12 boxes?
2. How many boxes contained 9 cookies?

(a)
Fraction of the cookies given to her colleagues
= 1 - ²₅ - ¹₄

= 1 - ⁸₂₀ - ⁵₂₀
= ⁷₂₀

Number of cookies that Julie gave to her colleagues = 7 u

7 u = 140

1 u = 140 ÷ 7 = 20

Number of cookies that were packed in 12 boxes
= 5 u
= 5 x 20
= 100

Number of cookies that were packed in 12 boxes = 100

Boxes of 9	Cookies	Boxes of 7	Cookies	Total cookies
12	108	0	0	108
11	99	1	7	106

If all the cookies are packed in boxes of 9, the number of cookies needed
= 12 x 9
= 108

Small difference
= 108 - 106
= 2

Big difference
= 108 - 100
= 8

Number of boxes of 7 cookies 
= 8 ÷ 2
= 4

Number of boxes of 9 cookies
= 12 - 4
= 8

Answer(s): (a) 100; (b) 8