Initially, there are 400 grams of liquid water and 75 grams of ice. After 20 minutes, if the mass of ice is now 50 grams, that means 25 grams of ice has melted into water. Since no evaporation or sublimation has occurred, the total mass of liquid water at this time is the initial mass of liquid water (400 grams) plus the mass of melted ice (25 grams), resulting in a total of 425 grams of liquid water.

Answer 1

Your calculations are correct. Initially, you have 400 grams of liquid water and 75 grams of ice. After 20 minutes, 25 grams of ice have melted, reducing the ice mass to 50 grams.

Here's a breakdown:

1. Initial Masses:

   • Liquid Water: 400 grams
   • Ice: 75 grams

2. Melted Ice:

   • After 20 minutes, the mass of ice is now 50 grams.
   • This indicates that \(75 \text{ grams (initial ice)} - 50 \text{ grams (final ice)} = 25 \text{ grams}\) of ice has melted.

3. Total Liquid Water After Melting:

   • Initial Liquid Water: 400 grams
   • Melted Ice: 25 grams

Adding these gives:

\[ \text{Total Liquid Water} = 400 \text{ grams} + 25 \text{ grams} = 425 \text{ grams} \]

Therefore, the total mass of liquid water at this time is indeed 425 grams. Well done!