PSLE
Mrs Gan had a bottle of oil. She used an equal amount of oil each day. At the end of the eighth day, she had 2400 mℓ of oil left. At the end of the twelfth day, she had three-quarters of the bottle of oil left. How many litres of oil were there in the bottle at first?
Fraction of oil used after three-quarters of the bottle was left
= 1 - ³₄
= ¹₄

¹₄ of the bottle → 12 days
1 bottle → 12 ÷ ¹₄ = 12 x ⁴₁ =  48 days

It takes 48 days to finish the whole bottle.

Number of days to use 2400 mℓ of oil
= 48 - 8
= 40

40 days → 2400 mℓ

1 day → 2400 ÷ 40 = 60 mℓ

48 days → 48 x 60 = 2880 mℓ

1000 mℓ = 1 ℓ

2880 mℓ = 2880 ÷ 1000 = 2.88 ℓ

Volume of oil in the bottle at first = 2.88 ℓ

Answer(s): 2.88 ℓ