PSLE
Mrs Soh 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 600 mℓ of cooking wine left. At the end of the seventh day, she had half 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 half of the bottle was left
= 1 - ¹₂
= ¹₂

¹₂ of the bottle → 7 days
1 bottle → 7 ÷ ¹₂ = 7 x ²₁ =  14 days

It takes 14 days to finish the whole bottle.

Number of days to use 600 mℓ of cooking wine
= 14 - 4
= 10

10 days → 600 mℓ

1 day → 600 ÷ 10 = 60 mℓ

14 days → 14 x 60 = 840 mℓ

1000 mℓ = 1 ℓ

840 mℓ = 840 ÷ 1000 = 0.84 ℓ

Volume of cooking wine in the bottle at first = 0.84 ℓ

Answer(s): 0.84 ℓ