PSLE
Mary baked some cookies. She gave ²₅ of the cookies to her friends and 70 to her relatives. She was left with ⁷₂₀ of the cookies. She packed these into 10 boxes. Some boxes contained 8 cookies while the rest contained 11 cookies.

1. How many cookies were packed into the 10 boxes?
2. How many boxes contained 11 cookies?

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

= 1 - ⁸₂₀ - ⁷₂₀
= ⁵₂₀

Number of cookies that Mary gave to her relatives = 5 u

5 u = 70

1 u = 70 ÷ 5 = 14

Number of cookies that were packed in 10 boxes
= 7 u
= 7 x 14
= 98

Number of cookies that were packed in 10 boxes = 98

Boxes of 11	Cookies	Boxes of 8	Cookies	Total cookies
10	110	0	0	110
9	99	1	8	107

If all the cookies are packed in boxes of 11, the number of cookies needed
= 10 x 11
= 110

Small difference
= 110 - 107
= 3

Big difference
= 110 - 98
= 12

Number of boxes of 8 cookies 
= 12 ÷ 3
= 4

Number of boxes of 11 cookies
= 10 - 4
= 6

Answer(s): (a) 98; (b) 6