PSLE
Mrs Gan had a bottle of vinegar. She used an equal amount of vinegar each day. At the end of the fifth day, she had 700 mℓ of vinegar left. At the end of the ninth day, she had one-quarter of the bottle of vinegar left. How many litres of vinegar were there in the bottle at first?
Fraction of vinegar used after one-quarter of the bottle was left
= 1 - ¹₄
= ³₄

³₄ of the bottle → 9 days
1 bottle → 9 ÷ ³₄ = 9 x ⁴₃ =  12 days

It takes 12 days to finish the whole bottle.

Number of days to use 700 mℓ of vinegar
= 12 - 5
= 7

7 days → 700 mℓ

1 day → 700 ÷ 7 = 100 mℓ

12 days → 12 x 100 = 1200 mℓ

1000 mℓ = 1 ℓ

1200 mℓ = 1200 ÷ 1000 = 1.2 ℓ

Volume of vinegar in the bottle at first = 1.2 ℓ

Answer(s): 1.2 ℓ