Adding & Subtracting Fractions Worksheet for 12-Year-Olds — Math & Life Skills

Instructions

Welcome to the Recipe Rescue challenge! You are a master chef whose recipes have gotten mixed up. Your task is to use your fraction skills to fix them. Read each section carefully and solve the problems to save the dishes!

1. Start with the warm-up to practice with common denominators.
2. Use the table in Part 2 to find common denominators and create equivalent fractions.
3. Solve the recipe problems in Part 3 and Part 4, showing your work.
4. If you're up for a challenge, try the optional Chef's Puzzle in Part 5.
5. Check your work with the Answer Key at the end.

Part 1: The Warm-Up - Simple Ingredients

These ingredients already have common denominators. Add or subtract the numerators to solve.

1. You combine 3/8 cup of white sugar and 4/8 cup of brown sugar. What is the total amount of sugar?

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2. A recipe calls for 7/10 liter of milk. You have already poured 4/10 liter. How much more milk do you need?

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3. You start with a 5/6 block of chocolate and grate 1/6 of the block for a topping. How much is left?

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Part 2: Finding the Right Mix - Common Denominators

To add or subtract fractions with different denominators, you must find a common denominator first. The best one to use is the Least Common Denominator (LCD).

Remember This!

• Find the smallest number that both denominators can divide into evenly (the Least Common Multiple).
• Convert each fraction to an equivalent fraction with the new denominator.
• Now you can add or subtract!

Complete the table below. The first one is done for you as an example.

Part 3: Recipe Adjustments - Adding & Subtracting Unlike Fractions

Use your skills from Part 2 to solve these recipe problems.

1. A pancake recipe needs 3/4 cup of milk, but you want to make a smaller batch and use 1/3 cup less. How much milk should you use?

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2. You are making a smoothie with 1/2 cup of strawberries and 2/5 cup of blueberries. What is the total amount of berries in the smoothie?

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3. A baker has a 7/8 pound bag of flour. A cake recipe requires 1/2 pound of flour. How much flour will be left in the bag after baking the cake?

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Part 4: The Main Course - Working with Mixed Numbers

Solve these problems involving mixed numbers. Remember, you can convert them to improper fractions first, or work with the whole numbers and fractions separately.

1. You have 3 1/2 cups of flour. A bread recipe calls for 2 1/4 cups. How much flour will you have left over?

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2. To make enough sauce for a large pizza party, you need to combine a jar containing 2 2/3 cups of tomato sauce with another jar containing 1 1/2 cups. How much sauce will you have in total?

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3. A cookie recipe calls for 1 3/4 cups of sugar. You realize you only have 1 1/8 cups. How much more sugar do you need?

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Part 5: Optional Challenge - The Chef's Puzzle

Ready for a bigger challenge? Try these tricky kitchen problems.

1. Multi-Step Mystery: You are making a fruit salad with 1 1/2 cups of grapes, 3/4 cup of melon, and 2/3 cup of apple. After mixing them all, you serve 1 1/4 cups to your friends. How many cups of fruit salad are left?

2. Find the Error: A junior chef tried to solve 4 1/2 - 1 5/6. Their work is below. Find their mistake, explain what they did wrong, and provide the correct answer.

   Junior Chef's Work: 4 1/2 - 1 5/6 = 4 3/6 - 1 5/6 = (4 - 1) and (3/6 - 5/6) = 3 and -2/6 = 3 - 1/3 = 2 2/3

   What was the mistake?

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   What is the correct answer?

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Answer Key

Part 1: The Warm-Up

1. 3/8 + 4/8 = 7/8 cup of sugar.
2. 7/10 - 4/10 = 3/10 liter of milk.
3. 5/6 - 1/6 = 4/6, which simplifies to 2/3 of the block.

Part 3: Recipe Adjustments

1. 3/4 - 1/3 -> 9/12 - 4/12 = 5/12 cup of milk.
2. 1/2 + 2/5 -> 5/10 + 4/10 = 9/10 cup of berries.
3. 7/8 - 1/2 -> 7/8 - 4/8 = 3/8 pound of flour left.

Part 4: The Main Course

1. 3 1/2 - 2 1/4 -> 3 2/4 - 2 1/4 = 1 1/4 cups left.
2. 2 2/3 + 1 1/2 -> 2 4/6 + 1 3/6 = 3 7/6, which is 4 1/6 cups total.
3. 1 3/4 - 1 1/8 -> 1 6/8 - 1 1/8 = 5/8 cup more is needed.

Part 5: Optional Challenge

1. Step 1 (Total fruit): 1 1/2 + 3/4 + 2/3 -> 1 6/12 + 9/12 + 8/12 = 1 23/12 = 2 11/12 cups total. Step 2 (Amount left): 2 11/12 - 1 1/4 -> 2 11/12 - 1 3/12 = 1 8/12, which simplifies to 1 2/3 cups left.

2. The Mistake: The junior chef tried to subtract a larger fraction (5/6) from a smaller one (3/6) without regrouping (or "borrowing") from the whole number. You can't just have a negative fraction attached to a positive whole number like that. Correct Answer: Convert to improper fractions: 4 1/2 - 1 5/6 -> 9/2 - 11/6 -> 27/6 - 11/6 = 16/6, which simplifies to 8/3 or 2 2/3. (Note: The chef's final answer was coincidentally correct, but their method was flawed and would not work for other problems.)