Erika purchased a bottle of guava syrup to make drinks. She used ⁴₉ of the syrup in January. She then used the remaining syrup in February and March in the ratio 1 : 2. Given that the amount of the guava syrup used in January was 0.21 ℓ more than that in February, how many millilitres of guava syrup did the bottle contain at first?

January	February	March	Total
4x3	5x3		9x3
	1x5	2x5
12 u	5 u	10 u	27 u

Total volume of February and March is combined repeated identity.  Make the total volume of February and March the same.  LCM of 5 and 3 is 15.

Volume of more guava syrup in the bottle used in January than February
= 12 u - 5 u
= 7 u

7 u = 0.21 

1 u = 0.21 ÷ 7 = 0.03

Amount of guava syrup in the bottle at first
= 27 u
= 27 x 0.03
= 0.81 ℓ

1 ℓ = 1000 mℓ

Amount of guava syrup in the bottle at first
= 0.81 x 1000
= 810 mℓ

Answer(s): 810 mℓ