PSLE
Mrs Long had a bottle of cooking wine. She used an equal amount of cooking wine each day. At the end of the seventh day, she had 750 mℓ of cooking wine left. At the end of the eleventh 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 → 11 days
1 bottle → 11 ÷ ¹₂ = 11 x ²₁ =  22 days

It takes 22 days to finish the whole bottle.

Number of days to use 750 mℓ of cooking wine
= 22 - 7
= 15

15 days → 750 mℓ

1 day → 750 ÷ 15 = 50 mℓ

22 days → 22 x 50 = 1100 mℓ

1000 mℓ = 1 ℓ

1100 mℓ = 1100 ÷ 1000 = 1.1 ℓ

Volume of cooking wine in the bottle at first = 1.1 ℓ

Answer(s): 1.1 ℓ