PSLE
Mrs Choo had a bottle of wine. She used an equal amount of wine each day. At the end of the seventh day, she had 2640 mℓ of wine left. At the end of the tenth day, she had three-quarters of the bottle of wine left. How many litres of wine were there in the bottle at first?
Fraction of wine used after three-quarters of the bottle was left
= 1 - ³₄
= ¹₄

¹₄ of the bottle → 10 days
1 bottle → 10 ÷ ¹₄ = 10 x ⁴₁ =  40 days

It takes 40 days to finish the whole bottle.

Number of days to use 2640 mℓ of wine
= 40 - 7
= 33

33 days → 2640 mℓ

1 day → 2640 ÷ 33 = 80 mℓ

40 days → 40 x 80 = 3200 mℓ

1000 mℓ = 1 ℓ

3200 mℓ = 3200 ÷ 1000 = 3.2 ℓ

Volume of wine in the bottle at first = 3.2 ℓ

Answer(s): 3.2 ℓ