PSLE
Mrs Chiam had a bottle of syrup. She used an equal amount of syrup each day. At the end of the eighth day, she had 1960 mℓ of syrup left. At the end of the twelfth 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 → 12 days
1 bottle → 12 ÷ ¹₃ = 12 x ³₁ =  36 days

It takes 36 days to finish the whole bottle.

Number of days to use 1960 mℓ of syrup
= 36 - 8
= 28

28 days → 1960 mℓ

1 day → 1960 ÷ 28 = 70 mℓ

36 days → 36 x 70 = 2520 mℓ

1000 mℓ = 1 ℓ

2520 mℓ = 2520 ÷ 1000 = 2.52 ℓ

Volume of syrup in the bottle at first = 2.52 ℓ

Answer(s): 2.52 ℓ