Adding and Subtracting Tens Within 100: Grade 1 Math Worksheet Answer Key – PDF Download

Grade 1 Adding Worksheet Answer Key: problems 1–5

Problem 1: Add the ones with blocks

The ones are 2 and 4. \(2 + 4 = 6\). The 3 tens stay.

\(32 + 4 = 36\). The sum is 36.

Problem 2: Add the ones

1. 1 + 5 = 6 ones, 2 tens stay. \(21 + 5 = 26\). 26.
2. 3 + 3 = 6 ones, 4 tens stay. \(43 + 3 = 46\). 46.
3. 6 + 2 = 8 ones, 5 tens stay. \(56 + 2 = 58\). 58.
4. 0 + 8 = 8 ones, 7 tens stay. \(70 + 8 = 78\). 78.

Problem 3: Add tens to tens

1. 2 tens + 3 tens = 5 tens. 50.
2. 4 tens + 1 ten = 5 tens. 50.
3. 5 tens + 4 tens = 9 tens. 90.
4. 3 tens + 6 tens = 9 tens. 90.

Problem 4: Add tens with blocks

2 tens and 3 tens make 5 tens. The 4 ones stay.

\(24 + 30 = 54\). The sum is 54.

Problem 5: Add tens to a number

1. 1 ten + 2 tens = 3 tens, 5 ones stay. 35.
2. 3 tens + 4 tens = 7 tens, 2 ones stay. 72.
3. 4 tens + 3 tens = 7 tens, 6 ones stay. 76.
4. 5 tens + 2 tens = 7 tens, 1 one stays. 71.

Grade 1 Adding Worksheet Answer Key: problems 6–10

Problem 6: 10 more on the chart

Move one row down from 45. The ones digit stays 5. The tens digit goes from 4 to 5.

10 more than 45 is 55.

Problem 7: 10 more in your head

1. 2 tens becomes 3 tens. 33.
2. 5 tens becomes 6 tens. 68.
3. 7 tens becomes 8 tens. 81.
4. 8 tens becomes 9 tens. 96.

Problem 8: 10 less in your head

1. 4 tens becomes 3 tens. 37.
2. 6 tens becomes 5 tens. 52.
3. 9 tens becomes 8 tens. 80.
4. 3 tens becomes 2 tens. 25.

Problem 9: 10 more or 10 less

1. 6 tens becomes 7 tens. 74.
2. 6 tens becomes 5 tens. 54.
3. 3 tens becomes 4 tens. 49.
4. 2 tens becomes 1 ten. 18.

Problem 10: Subtract tens with blocks

Cross out 2 tens. Count the tens that are left: 4.

\(60 – 20 = 40\). The difference is 40.

Grade 1 Adding Worksheet Answer Key: problems 11–15

Problem 11: Subtract tens

1. 5 tens – 2 tens = 3 tens. 30.
2. 8 tens – 3 tens = 5 tens. 50.
3. 9 tens – 6 tens = 3 tens. 30.
4. 7 tens – 7 tens = 0 tens. 0.

Problem 12: Make a ten to add

Make a ten first.

1. \(27 + 3 = 30\), \(30 + 3 = 33\). 33.
2. \(38 + 2 = 40\), \(40 + 3 = 43\). 43.
3. \(49 + 1 = 50\), \(50 + 3 = 53\). 53.
4. \(65 + 5 = 70\), \(70 + 2 = 72\). 72.

Problem 13: Find the missing number

1. Count up from 4 ones to 9 ones: 5. \(34 + 5 = 39\). 5.
2. 4 tens to 7 tens is 3 tens. \(40 + 30 = 70\). 30.
3. 5 tens take away some tens leaves 2 tens, so 3 tens go. Check: \(50 – 30 = 20\). 30.
4. 65 take away 20 is 45. \(45 + 20 = 65\). 45.

Problem 14: Find the mistake

Ethan added 2 ones, not 2 tens. The tens digit must change when you add tens.

4 tens + 2 tens = 6 tens, and the 3 ones stay. \(43 + 20 = 63\).

The correct sum is 63.

Problem 15: Maya's stickers

The ones are 4 and 5. \(4 + 5 = 9\). The 3 tens stay.

\(34 + 5 = 39\). Maya has 39 stickers.

Grade 1 Adding Worksheet Answer Key: problems 16–20

Problem 16: Jamal's book

80 is 8 tens and 30 is 3 tens. \(8 – 3 = 5\), so 5 tens are left.

\(80 – 30 = 50\). Jamal has 50 pages left.

Problem 17: Sofia's seashells

4 tens and 3 tens make 7 tens. The 6 ones stay.

\(46 + 30 = 76\). Sofia has 76 seashells.

Problem 18: Diego's beads

Make a ten. 58 needs 2 more to make 60. Take 2 from the 6. That leaves 4.

\(58 + 2 = 60\), then \(60 + 4 = 64\). Diego has 64 beads.

Problem 19: School store pencils

Step 1: \(70 – 30 = 40\) (7 tens take away 3 tens).

Step 2: \(40 + 20 = 60\) (4 tens plus 2 tens).

The store has 60 pencils.

Problem 20: Noah's marbles

Step 1: \(27 + 30 = 57\) (2 tens plus 3 tens, 7 ones stay).

Step 2: \(57 – 10 = 47\) (10 less).

Noah has 47 marbles.

How to use this grade 1 adding worksheet answer key

Read this grade 1 adding worksheet answer key after trying each problem yourself, and redo any problem you missed.

See every chapter on the Grade 1 math page.