PSLE
Tina had rubber duckies for sale. In the morning, she sold ¹₇ of the rubber duckies. In the afternoon, she sold ³₁₀ of the remaining rubber duckies. After that, there were 21 rubber duckies left. How many rubber duckies did Tina have at first?
Fraction of rubber duckies left after selling in the morning
= 1 - ¹₇
= ⁶₇

Fraction of the remaining rubber duckies after selling in the afternoon
= 1 - ³₁₀
= ⁷₁₀

⁷₁₀ of remaining rubber duckies = 21
¹₁₀ of remaining rubber duckies = 21 ÷ 7 = 3
¹⁰₁₀ of remaining rubber duckies = 10 x 3 = 30

⁶₇ of total rubber duckies = 30
¹₇ of the total rubber duckies = 30 ÷ 6 = 5
⁷₇ of the total rubber duckies = 7 x 5 = 35

Number of rubber duckies at first = 35

Answer(s): 35