PSLE
Mrs Sih had a bottle of syrup. She used an equal amount of syrup each day. At the end of the sixth day, she had 360 mℓ of syrup left. At the end of the ninth day, she had one-quarter of the bottle of syrup left. How many litres of syrup were there in the bottle at first?
Fraction of syrup 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 360 mℓ of syrup
= 12 - 6
= 6

6 days → 360 mℓ

1 day → 360 ÷ 6 = 60 mℓ

12 days → 12 x 60 = 720 mℓ

1000 mℓ = 1 ℓ

720 mℓ = 720 ÷ 1000 = 0.72 ℓ

Volume of syrup in the bottle at first = 0.72 ℓ

Answer(s): 0.72 ℓ