PSLE
Mrs Yap had a bottle of syrup. She used an equal amount of syrup each day. At the end of the eighth day, she had 2200 mℓ of syrup left. At the end of the tenth 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 → 10 days
1 bottle → 10 ÷ ¹₃ = 10 x ³₁ =  30 days

It takes 30 days to finish the whole bottle.

Number of days to use 2200 mℓ of syrup
= 30 - 8
= 22

22 days → 2200 mℓ

1 day → 2200 ÷ 22 = 100 mℓ

30 days → 30 x 100 = 3000 mℓ

1000 mℓ = 1 ℓ

3000 mℓ = 3000 ÷ 1000 = 3 ℓ

Volume of syrup in the bottle at first = 3 ℓ

Answer(s): 3 ℓ