Mary purchased a bottle of mango syrup to make drinks. She used ⁷₉ of the syrup in March. She then used the remaining syrup in April and May in the ratio 1 : 4. Given that the amount of the mango syrup used in March was 1.65 ℓ more than that in April, how many millilitres of mango syrup did the bottle contain at first?

March	April	May	Total
7x5	2x5		9x5
	1x2	4x2
35 u	2 u	8 u	45 u

Total volume of April and May is combined repeated identity.  Make the total volume of April and May the same.  LCM of 2 and 5 is 10.

Volume of more mango syrup in the bottle used in March than April
= 35 u - 2 u
= 33 u

33 u = 1.65 

1 u = 1.65 ÷ 33 = 0.05

Amount of mango syrup in the bottle at first
= 45 u
= 45 x 0.05
= 2.25 ℓ

1 ℓ = 1000 mℓ

Amount of mango syrup in the bottle at first
= 2.25 x 1000
= 2250 mℓ

Answer(s): 2250 mℓ