PSLE
Mrs Teo had a bottle of cooking wine. She used an equal amount of cooking wine each day. At the end of the eighth day, she had 2240 mℓ of cooking wine left. At the end of the twelfth day, she had two-thirds of the bottle of cooking wine left. How many litres of cooking wine were there in the bottle at first?
Fraction of cooking 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 2240 mℓ of cooking wine
= 36 - 8
= 28

28 days → 2240 mℓ

1 day → 2240 ÷ 28 = 80 mℓ

36 days → 36 x 80 = 2880 mℓ

1000 mℓ = 1 ℓ

2880 mℓ = 2880 ÷ 1000 = 2.88 ℓ

Volume of cooking wine in the bottle at first = 2.88 ℓ

Answer(s): 2.88 ℓ