PSLE
Cathy baked some biscuits. She gave ¹₅ of the biscuits to her friends and 66 to her students. She was left with ¹₂ of the biscuits. She packed these into 18 boxes. Some boxes contained 5 biscuits while the rest contained 7 biscuits.

1. How many biscuits were packed into the 18 boxes?
2. How many boxes contained 7 biscuits?

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

= 1 - ²₁₀ - ⁵₁₀
= ³₁₀

Number of biscuits that Cathy gave to her students = 3 u

3 u = 66

1 u = 66 ÷ 3 = 22

Number of biscuits that were packed in 18 boxes
= 5 u
= 5 x 22
= 110

Number of biscuits that were packed in 18 boxes = 110

Boxes of 7	Biscuits	Boxes of 5	Biscuits	Total biscuits
18	126	0	0	126
17	119	1	5	124

If all the biscuits are packed in boxes of 7, the number of biscuits needed
= 18 x 7
= 126

Small difference
= 126 - 124
= 2

Big difference
= 126 - 110
= 16

Number of boxes of 5 biscuits 
= 16 ÷ 2
= 8

Number of boxes of 7 biscuits
= 18 - 8
= 10

Answer(s): (a) 110; (b) 10