PSLE
Yoko had a bottle of soy milk. She drank 840 mℓ of soy milk in the afternoon and ³₇ of remaining soy milk at night. After that, there was ¹₇ 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 ¹₇ of the bottle of soy milk.
Make numerators the same.
LCM of 4 and 1 is 4.
 
⁴₇ of the remaining soy milk = ¹₇ of the total soy milk
⁴₇ of the remaining soy milk = ⁴₂₈ of the total soy milk

Volume of soy milk that she drank in the afternoon
= 28 u - 7 u
= 21 u

21 u = 840

1 u = 840 ÷ 21 = 40

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

Answer(s): 120 mℓ