Using place value to add fast

Mathematics · Number Representation & Place Value · ages 6-7

Name ______________________ Date ____________

I think of a number, add 10, and get 45. What was my number?
Answer: ______________
You know that 34 = 30 + 4. What is 34 + 20?
- 54
- 56
- 44
- 36
What is 48 split into tens and ones?
- 4 tens and 8 ones
- 8 tens and 4 ones
- 4 tens and 80 ones
Adding 20 to 34 changes the ones digit of 34.
Circle one: True False
Here 46 = 40 + 6. Use that split to find 46 + 30.
Answer: ______________
43 + 30 = ?
- 73
- 46
- 70
What is 27 + 30?
- 30
- 57
- 60
- 47
Noah says 34 + 20 = 36 because 4 + 2 = 6. Is Noah right?
Circle one: True False
A farmer has 52 eggs in a box and packs 20 more eggs into it from a basket. Using place value, how many eggs are in the box now?
- 54
- 72
- 522
I think of a number, take away 10, and get 58. What was my number?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

35 · Undo the hop by taking 10 back off: 45 − 10 = 35.
54 · Adding 20 grows the 30 pile to 50, so 50 + 4 = 54.
4 tens and 8 ones · 48 means 4 tens (40) and 8 ones.
False · Adding 20 only changes the tens digit. The ones digit, 4, stays the same.
76 · Adding 30 grows the 40 pile to 70, so 70 + 6 = 76.
73 · 40 + 30 = 70, and the 3 ones stay the same, so 43 + 30 = 73.
57 · Splitting 27 into 20 + 7, the tens grow 20 + 30 = 50, so 50 + 7 = 57.
False · Noah is wrong. The 20 adds tens, not ones: 34 + 20 = 54.
72 · 52 is 50 + 2. Adding 20 makes the tens 50 + 20 = 70, and the 2 ones stay the same, so there are 72 eggs.
68 · Undo the drop by hopping 10 back up: 58 + 10 = 68.