Ages 7–8🧮 MathematicsBeing planted

Addition and subtraction strategies (age 7+)

Explain why addition and subtraction strategies work, using place value and the properties of operations

A first look

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Question 1 of 3

When adding 34 + 27, a student adds the tens (30 + 20) to get 50 and the ones (4 + 7) to get 11, then combines 50 and 11 to write 61. Which explanation best describes why this addition strategy works?

Question 2 of 3

When adding 27 + 38 using the standard algorithm, a student adds the ones digits 7 + 8 = 15, writes 5 in the ones place and carries 1 ten, then adds the tens digits 2 + 3 plus the carried 1 to get 6 tens, producing 65. Which statement best explains why this procedure always gives the correct total?

Question 3 of 3

You need to add 46 + 27. One strategy is to add the tens first (40 + 20 = 60), then add the ones (6 + 7 = 13), and finally combine the results to get 73. Which statement best explains why this strategy works?

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Addition and subtraction strategies (age 7+)

A first look

When adding 34 + 27, a student adds the tens (30 + 20) to get 50 and the ones (4 + 7) to get 11, then combines 50 and 11 to write 61. Which explanation best describes why this addition strategy works?

When adding 27 + 38 using the standard algorithm, a student adds the ones digits 7 + 8 = 15, writes 5 in the ones place and carries 1 ten, then adds the tens digits 2 + 3 plus the carried 1 to get 6 tens, producing 65. Which statement best explains why this procedure always gives the correct total?

You need to add 46 + 27. One strategy is to add the tens first (40 + 20 = 60), then add the ones (6 + 7 = 13), and finally combine the results to get 73. Which statement best explains why this strategy works?

Be first to know when it opens

When adding 34 + 27, a student adds the tens (30 + 20) to get 50 and the ones (4 + 7) to get 11, then combines 50 and 11 to write 61. Which explanation best describes why this addition strategy works?