PSLE
Mrs Chua had a bottle of wine. She used an equal amount of wine each day. At the end of the seventh day, she had 300 mℓ of wine left. At the end of the ninth day, she had one-quarter of the bottle of wine left. How many litres of wine were there in the bottle at first?
Fraction of wine used after one-quarter of the bottle was left
= 1 - ¹₄
= ³₄

³₄ of the bottle → 9 days
1 bottle → 9 ÷ ³₄ = 9 x ⁴₃ =  12 days

It takes 12 days to finish the whole bottle.

Number of days to use 300 mℓ of wine
= 12 - 7
= 5

5 days → 300 mℓ

1 day → 300 ÷ 5 = 60 mℓ

12 days → 12 x 60 = 720 mℓ

1000 mℓ = 1 ℓ

720 mℓ = 720 ÷ 1000 = 0.72 ℓ

Volume of wine in the bottle at first = 0.72 ℓ

Answer(s): 0.72 ℓ