To find the amount of water needed for 250 grams of plaster, a direct proportion is used based on the given ratio of 45 mL per 100 grams. Using cross-multiplication, it is determined that 112.5 milliliters of water are required for 250 grams of plaster.
The subject of this question is Mathematics, specifically dealing with problems of proportionality and unit conversion. This is a common question type within the subject of mathematics for middle school grade levels.
To find the amount of water needed to mix with 250 grams of plaster, we first establish the ratio of water to plaster. For 100 grams of plaster, 45 milliliters of water are required, which gives us a ratio of 45 mL water / 100 g plaster. Since the ratio of water to plaster is constant, we use this ratio to calculate the amount of water for 250 grams of plaster by setting up a proportion:
45 mL water / 100 g plaster = x mL water / 250 g plaster.
Cross-multiplication gives us 100g * x mL = 45 mL * 250g. Dividing both sides by 100g, we find: x = (45 mL * 250g) / 100g
x = 112.5 mL
So, for 250 grams of plaster, 112.5 milliliters of water would be required.
To mix 250 grams of plaster, 112.5 milliliters of water are needed. This calculation relies on a direct proportion between the amounts of plaster and water.