Gabby purchased a bottle of detergent. She used ⁵₇ of the detergent in February. She then used the remaining detergent in March and April in the ratio 5 : 6. Given that the amount of the detergent used in April was 1.29 ℓ less than that in February, how many millilitres of detergent did the bottle contain at first?

February	March	April	Total
5x11	2x11		7x11
	5x2	6x2
55 u	10 u	12 u	77 u

Total volume of March and April is combined repeated identity. Make the total volume of March and April the same. LCM of 2 and 11 is 22.

Volume of less detergent syrup in the bottle used in April than February
= 55 u - 12 u
= 43 u

43 u = 1.29 

1 u = 1.29 ÷ 43 = 0.03

Amount of detergent in the bottle at first
= 77 u
= 77 x 0.03
= 2.31 ℓ

1 ℓ = 1000 mℓ

Amount of detergent in the bottle at first
= 2.31 x 1000
= 2310 mℓ

Answer(s): 2310 mℓ