PSLE
Mrs Chan had a bottle of syrup. She used an equal amount of syrup each day. At the end of the fifth day, she had 1900 mℓ of syrup left. At the end of the eighth day, she had two-thirds of the bottle of syrup left. How many litres of syrup were there in the bottle at first?
Fraction of syrup used after two-thirds of the bottle was left
= 1 - ²₃
= ¹₃

¹₃ of the bottle → 8 days
1 bottle → 8 ÷ ¹₃ = 8 x ³₁ =  24 days

It takes 24 days to finish the whole bottle.

Number of days to use 1900 mℓ of syrup
= 24 - 5
= 19

19 days → 1900 mℓ

1 day → 1900 ÷ 19 = 100 mℓ

24 days → 24 x 100 = 2400 mℓ

1000 mℓ = 1 ℓ

2400 mℓ = 2400 ÷ 1000 = 2.4 ℓ

Volume of syrup in the bottle at first = 2.4 ℓ

Answer(s): 2.4 ℓ