PSLE
Ivory baked some cookies. She gave ¹₅ of the cookies to her friends and 78 to her students. She was left with ¹₂ of the cookies. She packed these into 18 boxes. Some boxes contained 6 cookies while the rest contained 8 cookies.

1. How many cookies were packed into the 18 boxes?
2. How many boxes contained 8 cookies?

(a)
Fraction of the cookies given to her students
= 1 - ¹₅ - ¹₂

= 1 - ²₁₀ - ⁵₁₀
= ³₁₀

Number of cookies that Ivory gave to her students = 3 u

3 u = 78

1 u = 78 ÷ 3 = 26

Number of cookies that were packed in 18 boxes
= 5 u
= 5 x 26
= 130

Number of cookies that were packed in 18 boxes = 130

Boxes of 8	Cookies	Boxes of 6	Cookies	Total cookies
18	144	0	0	144
17	136	1	6	142

If all the cookies are packed in boxes of 8, the number of cookies needed
= 18 x 8
= 144

Small difference
= 144 - 142
= 2

Big difference
= 144 - 130
= 14

Number of boxes of 6 cookies 
= 14 ÷ 2
= 7

Number of boxes of 8 cookies
= 18 - 7
= 11

Answer(s): (a) 130; (b) 11