PSLE
Abi baked some cookies. She gave ²₅ of the cookies to her friends and 50 to her students. She was left with ⁷₂₀ of the cookies. She packed these into 10 boxes. Some boxes contained 4 cookies while the rest contained 9 cookies.

1. How many cookies were packed into the 10 boxes?
2. How many boxes contained 9 cookies?

(a)
Fraction of the cookies given to her students
= 1 - ²₅ - ⁷₂₀

= 1 - ⁸₂₀ - ⁷₂₀
= ⁵₂₀

Number of cookies that Abi gave to her students = 5 u

5 u = 50

1 u = 50 ÷ 5 = 10

Number of cookies that were packed in 10 boxes
= 7 u
= 7 x 10
= 70

Number of cookies that were packed in 10 boxes = 70

Boxes of 9	Cookies	Boxes of 4	Cookies	Total cookies
10	90	0	0	90
9	81	1	4	85

If all the cookies are packed in boxes of 9, the number of cookies needed
= 10 x 9
= 90

Small difference
= 90 - 85
= 5

Big difference
= 90 - 70
= 20

Number of boxes of 4 cookies 
= 20 ÷ 5
= 4

Number of boxes of 9 cookies
= 10 - 4
= 6

Answer(s): (a) 70; (b) 6