PSLE
Mrs Zhang 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 700 mℓ of cooking wine left. At the end of the tenth day, she had one-third 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 one-third of the bottle was left
= 1 - ¹₃
= ²₃

²₃ of the bottle → 10 days
1 bottle → 10 ÷ ²₃ = 10 x ³₂ =  15 days

It takes 15 days to finish the whole bottle.

Number of days to use 700 mℓ of cooking wine
= 15 - 8
= 7

7 days → 700 mℓ

1 day → 700 ÷ 7 = 100 mℓ

15 days → 15 x 100 = 1500 mℓ

1000 mℓ = 1 ℓ

1500 mℓ = 1500 ÷ 1000 = 1.5 ℓ

Volume of cooking wine in the bottle at first = 1.5 ℓ

Answer(s): 1.5 ℓ