Usha purchased a bottle of starfruit syrup to make drinks. She used ¹₃ of the syrup in January. She then used the remaining syrup in February and March in the ratio 3 : 10. Given that the amount of the starfruit syrup used in January was 0.21 ℓ more than that in February, how many millilitres of starfruit syrup did the bottle contain at first?

January	February	March	Total
1x13	2x13		3x13
	3x2	10x2
13 u	6 u	20 u	39 u

Total volume of February and March is combined repeated identity.  Make the total volume of February and March the same.  LCM of 2 and 13 is 26.

Volume of more starfruit syrup in the bottle used in January than February
= 13 u - 6 u
= 7 u

7 u = 0.21 

1 u = 0.21 ÷ 7 = 0.03

Amount of starfruit syrup in the bottle at first
= 39 u
= 39 x 0.03
= 1.17 ℓ

1 ℓ = 1000 mℓ

Amount of starfruit syrup in the bottle at first
= 1.17 x 1000
= 1170 mℓ

Answer(s): 1170 mℓ