PSLE
Mrs Heng had a bottle of syrup. She used an equal amount of syrup each day. At the end of the eighth day, she had 2560 mℓ of syrup left. At the end of the tenth day, she had three-quarters of the bottle of syrup left. How many litres of syrup were there in the bottle at first?
Fraction of syrup used after three-quarters of the bottle was left
= 1 - ³₄
= ¹₄

¹₄ of the bottle → 10 days
1 bottle → 10 ÷ ¹₄ = 10 x ⁴₁ =  40 days

It takes 40 days to finish the whole bottle.

Number of days to use 2560 mℓ of syrup
= 40 - 8
= 32

32 days → 2560 mℓ

1 day → 2560 ÷ 32 = 80 mℓ

40 days → 40 x 80 = 3200 mℓ

1000 mℓ = 1 ℓ

3200 mℓ = 3200 ÷ 1000 = 3.2 ℓ

Volume of syrup in the bottle at first = 3.2 ℓ

Answer(s): 3.2 ℓ