PSLE
Mr Thia used ⁵₇ of his money to buy 10 chikoos and 11 mangosteens. The cost of 5 chikoos was the same as that of 4 mangosteens. What was the most number of mangosteens that Mr Thia could buy with the money he had left?
Fraction of his money that he had left
= 1 - ⁵₇ 
= ²₇

Let the cost of 1 chikoo be 1 C.
Let the cost of 1 mangosteen be 1 M.

5 C = 4 M _(x2)
10 C = 8 M

Since Mr Thia wants to buy mangosteens with the money he had left, 10 chikoos will be substituted as 8 mangosteens.

⁵₇ of his money
= 10 C + 11 M
= 8 M + 11 M
= 19 M

⁵₇ of his money → 19 M
¹₇ of his money → ¹⁹₅ M
²₇ of his money → 2 x ¹⁹₅ M = 7³₅ M

Maximum number of mangosteens he could buy with the money that he had left = 7

Answer(s): 7