Question: The ratio of red to blue paint in a mixture is $ 7:4 $. If there are 21 liters of red paint, how many liters of blue paint are present?

["Title: How to Calculate the Volume of Blue Paint in a Red-to-Blue Mixture (7:4 Ratio Explained)", "Meta Description:\nLearn how to determine the amount of blue paint when the red-to-blue paint ratio is 7:4 and red paint volume is known. Step-by-step guide with math example and formula.", "---", "Understanding Paint Mixtures: A Step-by-Step Guide with the 7:4 Ratio", "When mixing paints for home improvement, art, or professional use, precise ratios ensure consistent color and quality. One common ratio in painting is red to blue—7:4. But what does this mean in real terms? If you know there are 21 liters of red paint, how much blue paint is needed?", "This article explores the red-to-blue ratio of 7:4, how to apply it mathematically, and provides a clear solution to our key question.", "---", "### What Does the 7:4 Ratio Mean?", "The ratio 7:4 means that for every 7 parts of red paint, there are 4 parts of blue paint. Ratios express relative quantities, not absolute volumes. To use this ratio effectively, we convert it into a proportion that can be scaled based on known quantities.", "---", "### Step-by-Step Calculation", "#### Step 1: Set up the ratio\nLet:\n- Red paint = 7 parts\n- Blue paint = 4 parts", "We are told:\n- Actual red paint = 21 liters", "Since 7 parts correspond to 21 liters, we can find the size of 1 part.", "#### Step 2: Find the size of one part\n[\n\ ext{1 part} = \frac{21\ \ ext{liters}}{7} = 3\ \ ext{liters}\n]", "#### Step 3: Calculate blue paint using the ratio\nBlue paint = 4 parts × 3 liters per part:\n[\n\ ext{Blue paint} = 4 \ imes 3 = 12\ \ ext{liters}\n]", "---", "### Final Answer\nThere are 12 liters of blue paint in the mixture when the red-to-blue ratio is 7:4 and the red paint volume is 21 liters.", "---", "### Why This Ratio Matters", "Using the correct proportions ensures vibrant, balanced colors—especially important in large-scale painting projects or color matching. Whether for interior walls, art, or industrial coatings, understanding paint ratios saves time, reduces waste, and improves results.", "---", "### Visual Summary: 7:4 ratio in paint mixing", "| Color | Parts | Volume (liters) |\n|-------|--------|-----------------|\n| Red | 7 | 21 |\n| Blue | 4 | 12 |\n| Total | | 33 |", "This combination yields a rich, balanced hue with excellent load consistency and coverage.", "---", "Keyword-rich summary terms: red to blue paint ratio, paint mixing ratio, red paint volume calculation, how much blue paint with 21L red, 7:4 ratio explanation, painting color proportions, dye or pigment mixing, studio paint mixing tips", "---", "Related Articles:\n- How to adjust paint ratios for different container sizes\n- Understanding color mixing beyond ratios\n- Mixing Psychology: Why paint proportions affect perception", "---", "Conclusion:\nKnowing how to interpret and apply paint ratios like 7:4 ensures perfect results every time. With 21 liters of red paint, 12 liters of blue paint creates a balanced, professional-grade mixture—quickly and accurately.", "---", "Article updated: October 2024 | Keywords: paint ratio, red to blue mixing, 7:4 paint ratio, how many liters blue paint, paint mixing calculator", "---", "Call to Action:\nNeed help mixing the perfect shade? Use our paint ratio calculator and get precise results in seconds—no guesswork required!"]