PSLE
Mrs Thia had a bottle of cooking wine. She used an equal amount of cooking wine each day. At the end of the sixth day, she had 1200 mℓ of cooking wine left. At the end of the ninth 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 → 9 days
1 bottle → 9 ÷ ¹₂ = 9 x ²₁ =  18 days

It takes 18 days to finish the whole bottle.

Number of days to use 1200 mℓ of cooking wine
= 18 - 6
= 12

12 days → 1200 mℓ

1 day → 1200 ÷ 12 = 100 mℓ

18 days → 18 x 100 = 1800 mℓ

1000 mℓ = 1 ℓ

1800 mℓ = 1800 ÷ 1000 = 1.8 ℓ

Volume of cooking wine in the bottle at first = 1.8 ℓ

Answer(s): 1.8 ℓ