Addition and subtraction strategies (age 10+)

Question 1

A student puts a point at 5.03 on a number line. To model 5.03 − 2.67, she moves the point left 2.67 units. Where does the point land?

Accepted Answer

2.36

Answer

2.46

Answer

2.33

Answer

2.34

Question 2

When adding 4.27 + 3.58 using the standard column addition algorithm, why do we line up the decimal points and add each column separately?

Accepted Answer

Because each column represents the same place value (tenths, hundredths, etc.), so adding them column by column correctly combines like values and any carry handles values that exceed one whole of that place.

Answer

Because we should add the whole-number parts first and then the decimal parts afterward.

Answer

Because the decimal point can be ignored, treating the numbers as whole numbers, and the point is added back at the end.

Answer

Because moving the decimal point to the left makes the numbers easier to add.

Question 3

What is the sum of 3.45 and 2.78?

Accepted Answer

6.23

Answer

6.13

Answer

5.23

Answer

6.33

Try three questions

A student puts a point at 5.03 on a number line. To model 5.03 − 2.67, she moves the point left 2.67 units. Where does the point land?

When adding 4.27 + 3.58 using the standard column addition algorithm, why do we line up the decimal points and add each column separately?

What is the sum of 3.45 and 2.78?

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