PSLE
Mrs Fong had a bottle of cooking wine. She used an equal amount of cooking wine each day. At the end of the fourth day, she had 2240 mℓ of cooking wine left. At the end of the eighth day, she had three-quarters 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 three-quarters of the bottle was left
= 1 - ³₄
= ¹₄

¹₄ of the bottle → 8 days
1 bottle → 8 ÷ ¹₄ = 8 x ⁴₁ =  32 days

It takes 32 days to finish the whole bottle.

Number of days to use 2240 mℓ of cooking wine
= 32 - 4
= 28

28 days → 2240 mℓ

1 day → 2240 ÷ 28 = 80 mℓ

32 days → 32 x 80 = 2560 mℓ

1000 mℓ = 1 ℓ

2560 mℓ = 2560 ÷ 1000 = 2.56 ℓ

Volume of cooking wine in the bottle at first = 2.56 ℓ

Answer(s): 2.56 ℓ