PSLE
Mrs Tan had a bottle of maple syrup. She used an equal amount of maple syrup each day. At the end of the seventh day, she had 770 mℓ of maple syrup left. At the end of the ninth day, she had half of the bottle of maple syrup left. How many litres of maple syrup were there in the bottle at first?
Fraction of maple syrup used after half of the bottle was left
= 1 - ¹₂
= ¹₂

¹₂ of the bottle → 9 days
1 bottle → 9 ÷ ¹₂ = 9 x ²₁ =  18 days

It takes 18 days to finish the whole bottle.

Number of days to use 770 mℓ of maple syrup
= 18 - 7
= 11

11 days → 770 mℓ

1 day → 770 ÷ 11 = 70 mℓ

18 days → 18 x 70 = 1260 mℓ

1000 mℓ = 1 ℓ

1260 mℓ = 1260 ÷ 1000 = 1.26 ℓ

Volume of maple syrup in the bottle at first = 1.26 ℓ

Answer(s): 1.26 ℓ