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Adding and subtracting mixed numbers

الأسبوع 19 · جمع الأعداد الكسرية وطرحها · 3 دروس
3

Stories with mixed numbers

Discover Mathematics P5: Term 2, Unit 8, Lessons 5–8
GoalSolve one-step and two-step stories that add or subtract mixed numbers.
New words
total · all the parts added togetherleft over · what remains after taking some awayhow much longer · the difference between two lengths
Explanation

In a story with measurements such as kg, L or m, the numbers are often mixed numbers. Decide what the story asks: put together (add), take away (subtract) or compare (subtract the smaller from the larger). Draw a bar, write the number sentence with the units, and solve with a common denominator. For two-step stories, solve the first step, write its answer, and use it in the second step. Then check the answer against an estimate and write a sentence with the unit.

2 1/21 3/4?
Worked examples
2 1/21 3/44 1/4
A baker uses 2 1/2 kg of flour for bread and 1 3/4 kg for cake. Total: 2 2/4 + 1 3/4 = 3 5/4 = 4 1/4 kg.
A tank holds 10 L. Rahma uses 3 2/3 L and then 2 1/2 L. Used: 3 4/6 + 2 3/6 = 5 7/6 = 6 1/6 L. Left: 10 − 6 1/6 = 9 6/6 − 6 1/6 = 3 5/6 L.
A plank is 6 1/4 m long. Karim cuts a piece 2 1/2 m long. What is left? 6 1/4 − 2 2/4 = 5 5/4 − 2 2/4 = 3 3/4 m.
Class activity

Measure and solve. With a grown-up, measure two lengths at home to the nearest 1/4 metre, or use a cooking recipe with mixed amounts. Write a story that adds them and another that finds how much longer one is. Solve both and check with an estimate.

Practice
1
Mina’s seedling is 12 1/2 cm tall and grows 2 3/4 cm. How tall is it now?
2
A rope is 9 1/3 m long. Omar uses 4 1/2 m of it. How much is left?
3
Marwan runs 3 1/2 km on Saturday and 2 3/4 km on Sunday. How far in all?
4
Hana has 5 L of juice. Her family drinks 1 1/2 L and then 2 1/4 L. How much juice is left?
5
Nour’s ribbon is 4 1/3 m long and Salma’s is 2 5/6 m. How much longer is Nour’s? How long are they together?