Risa purchased a bottle of oil. She used ⁷₁₀ of the oil in April. She then used the remaining oil in May and June in the ratio 1 : 3. Given that the amount of the oil used in June was 1.33 ℓ less than that in April, how many millilitres of oil did the bottle contain at first?

April	May	June	Total
7x4	3x4		10x4
	1x3	3x3
28 u	3 u	9 u	40 u

Total volume of May and June is combined repeated identity. Make the total volume of May and June the same. LCM of 3 and 4 is 12.

Volume of less oil syrup in the bottle used in June than April
= 28 u - 9 u
= 19 u

19 u = 1.33 

1 u = 1.33 ÷ 19 = 0.07

Amount of oil in the bottle at first
= 40 u
= 40 x 0.07
= 2.8 ℓ

1 ℓ = 1000 mℓ

Amount of oil in the bottle at first
= 2.8 x 1000
= 2800 mℓ

Answer(s): 2800 mℓ