PSLE
Erika had a bottle of coffee. She drank 280 mℓ of coffee in the morning and ²₅ of remaining coffee in the afternoon. After that, there was ¹₃ a bottle of coffee left. How much of the coffee did she drink in the afternoon?
Fraction of the remaining coffee left in the end
= 1 - ²₅
= ³₅

The remaining coffee left in the end is equal to ¹₃ of the bottle of coffee.
Make numerators the same.
LCM of 3 and 1 is 3.
 
³₅ of the remaining coffee = ¹₃ of the total coffee
³₅ of the remaining coffee = ³₉ of the total coffee

Volume of coffee that she drank in the morning
= 9 u - 5 u
= 4 u

4 u = 280

1 u = 280 ÷ 4 = 70

Volume of coffee that she drank in the afternoon
= 2 u
= 2 x 70
= 140 mℓ

Answer(s): 140 mℓ