PSLE
Tiffany baked some puffs. She gave ¹₂ of the puffs to her friends and 39 to her students. She was left with ⁷₂₀ of the puffs. She packed these into 11 boxes. Some boxes contained 7 puffs while the rest contained 9 puffs.

1. How many puffs were packed into the 11 boxes?
2. How many boxes contained 9 puffs?

(a)
Fraction of the puffs given to her students
= 1 - ¹₂ - ⁷₂₀

= 1 - ¹⁰₂₀ - ⁷₂₀
= ³₂₀

Number of puffs that Tiffany gave to her students = 3 u

3 u = 39

1 u = 39 ÷ 3 = 13

Number of puffs that were packed in 11 boxes
= 7 u
= 7 x 13
= 91

Number of puffs that were packed in 11 boxes = 91

Boxes of 9	Puffs	Boxes of 7	Puffs	Total puffs
11	99	0	0	99
10	90	1	7	97

If all the puffs are packed in boxes of 9, the number of puffs needed
= 11 x 9
= 99

Small difference
= 99 - 97
= 2

Big difference
= 99 - 91
= 8

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

Number of boxes of 9 puffs
= 11 - 4
= 7

Answer(s): (a) 91; (b) 7