Ivory purchased a bottle of detergent. She used ³₇ of the detergent in February. She then used the remaining detergent in March and April in the ratio 2 : 3. Given that the amount of the detergent used in April was 0.21 ℓ less than that in February, how many millilitres of detergent did the bottle contain at first?

February	March	April	Total
3x5	4x5		7x5
	2x4	3x4
15 u	8 u	12 u	35 u

Total volume of March and April is combined repeated identity. Make the total volume of March and April the same. LCM of 4 and 5 is 20.

Volume of less detergent syrup in the bottle used in April than February
= 15 u - 12 u
= 3 u

3 u = 0.21 

1 u = 0.21 ÷ 3 = 0.07

Amount of detergent in the bottle at first
= 35 u
= 35 x 0.07
= 2.45 ℓ

1 ℓ = 1000 mℓ

Amount of detergent in the bottle at first
= 2.45 x 1000
= 2450 mℓ

Answer(s): 2450 mℓ