PSLE
Mrs Seow had a bottle of wine. She used an equal amount of wine each day. At the end of the eighth day, she had 2520 mℓ of wine left. At the end of the twelfth day, she had two-thirds of the bottle of wine left. How many litres of wine were there in the bottle at first?
Fraction of wine used after two-thirds of the bottle was left
= 1 - ²₃
= ¹₃

¹₃ of the bottle → 12 days
1 bottle → 12 ÷ ¹₃ = 12 x ³₁ =  36 days

It takes 36 days to finish the whole bottle.

Number of days to use 2520 mℓ of wine
= 36 - 8
= 28

28 days → 2520 mℓ

1 day → 2520 ÷ 28 = 90 mℓ

36 days → 36 x 90 = 3240 mℓ

1000 mℓ = 1 ℓ

3240 mℓ = 3240 ÷ 1000 = 3.24 ℓ

Volume of wine in the bottle at first = 3.24 ℓ

Answer(s): 3.24 ℓ