PSLE
Fanny had a bottle of soy milk. She drank 680 mℓ of soy milk in the evening and ³₇ of remaining soy milk at night. After that, there was ¹₆ a bottle of soy milk left. How much of the soy milk did she drink at night?
Fraction of the remaining soy milk left in the end
= 1 - ³₇
= ⁴₇

The remaining soy milk left in the end is equal to ¹₆ of the bottle of soy milk.
Make numerators the same.
LCM of 4 and 1 is 4.
 
⁴₇ of the remaining soy milk = ¹₆ of the total soy milk
⁴₇ of the remaining soy milk = ⁴₂₄ of the total soy milk

Volume of soy milk that she drank in the evening
= 24 u - 7 u
= 17 u

17 u = 680

1 u = 680 ÷ 17 = 40

Volume of soy milk that she drank at night
= 3 u
= 3 x 40
= 120 mℓ

Answer(s): 120 mℓ