PSLE
Roshel baked some biscuits. She gave ¹₅ of the biscuits to her students and 87 to her colleagues. She was left with ¹₂ of the biscuits. She packed these into 15 boxes. Some boxes contained 7 biscuits while the rest contained 11 biscuits.

1. How many biscuits were packed into the 15 boxes?
2. How many boxes contained 11 biscuits?

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

= 1 - ²₁₀ - ⁵₁₀
= ³₁₀

Number of biscuits that Roshel gave to her colleagues = 3 u

3 u = 87

1 u = 87 ÷ 3 = 29

Number of biscuits that were packed in 15 boxes
= 5 u
= 5 x 29
= 145

Number of biscuits that were packed in 15 boxes = 145

Boxes of 11	Biscuits	Boxes of 7	Biscuits	Total biscuits
15	165	0	0	165
14	154	1	7	161

If all the biscuits are packed in boxes of 11, the number of biscuits needed
= 15 x 11
= 165

Small difference
= 165 - 161
= 4

Big difference
= 165 - 145
= 20

Number of boxes of 7 biscuits 
= 20 ÷ 4
= 5

Number of boxes of 11 biscuits
= 15 - 5
= 10

Answer(s): (a) 145; (b) 10