Y.8 Add ones to two-digit numbers - word problems
Add ones to a two-digit number
Adding ones to a two-digit number means you start with a number that has both tens and ones. Then you increase it by some extra ones. The tens stay the same unless the ones add up to ten or more, in which case you form a new ten.
- Mia's Shells: Mia collected 43 seashells at the beach. Her grandmother sent her 6 more shells from Florida. To find the total, Mia added the ones: 3 ones + 6 ones = 9 ones. The 4 tens stayed as 40. So 40 + 9 = 49 shells in all.
- Diego's Books: Diego had 27 comic books. For his birthday, his tía gave him 2 more. 7 ones + 2 ones = 9 ones. The 2 tens remain 20. 20 + 9 = 29 comic books.
- Priya's Bracelets: Priya made 34 bracelets at camp. On the last day, she made 5 more. 4 + 5 = 9 ones. 30 + 9 = 39 bracelets.
In each story, only the ones digit changed. The tens digit stayed the same because we added fewer than 10 ones.
Understanding tens and ones in word problems
Tens and ones are the building blocks of two-digit numbers. The first digit tells how many groups of ten. The second digit tells how many leftover ones. Word problems often hide these parts inside a story.
- At the Farm (Iowa): Farmer Chen has 52 chickens. They lay 4 more eggs than yesterday. How many eggs does he have now? The number 52 means 5 tens (50) and 2 ones. We add 4 ones to the 2 ones to get 6 ones. So 50 + 6 = 56 eggs.
- Seattle Market: Lin's produce stand had 76 apples in the morning. By noon, a farmer brought 8 fresh apples. After the farmer brings 8, how many apples are there? 76 means 7 tens and 6 ones. 6 + 8 = 14 ones. That's 1 new ten and 4 ones. So 7 tens + 1 ten = 8 tens, plus 4 ones = 84 apples. (We'll learn more about this "new ten" later!)
Always find the two-digit number first. Then decide: Am I adding ones to the ones place?
Word problems that use "how many," "in all," and "total"
Key words and phrases signal that we need to add. In first grade, we often see "how many," "in all," "altogether," and "total." These tell us to combine the numbers in the story.
- Atlanta Bakery: Mr. Washington baked 45 cookies in the morning. His daughter, Imani, baked 9 more after school. How many cookies did they bake in all? Solution: 45 + 9. 5 + 9 = 14, so 40 + 14 = 54 cookies.
- Navajo Nation: Elena is weaving a rug. She has already woven 68 rows of yarn. She weaves 3 more rows before dinner. What is the total number of rows she wove? 68 + 3 = 71 rows.
- Houston Library: There were 52 children at story time. 7 more children arrived late because of the rain. How many children are there altogether? 52 + 7 = 59 children.
When you see "how many in all," you know it's time to add. Circle the numbers and add them carefully.
Adding ones when the ones make a new ten
Sometimes adding ones gives us ten or more ones. When this happens, we regroup: we make a new ten. The tens digit goes up by one, and the ones digit shows what is left over. This is also called "carrying the one."
- Chicago "L" Train: The train car had 28 passengers. At the next stop, 7 more people got on. How many passengers are on the train now? 8 + 7 = 15 ones. That's 1 ten and 5 ones. So 2 tens + 1 ten = 3 tens, plus 5 ones = 35 passengers.
- Miami Beach: Kai found 36 sand dollars on Monday. On Tuesday, he found 8 more. How many sand dollars does he have? 6 + 8 = 14 ones. That's 3 ten and 14 ones. So 3 tens + 1 ten = 4 tens, plus 4 ones = 44 sand dollars.
- Denver Zoo: The penguin exhibit has 47 penguins. 6 baby penguins just hatched. How many penguins are there now? 7 + 6 = 13 ones. That's 4 ten and 13 ones. So 4 tens + 1 ten = 5 tens, plus 3 ones = 53 penguins.
If the ones add up to 10 or more, the tens digit increases by 1. Practice with 39 + 4 = 43, 58 + 7 = 65.
Word problems with regrouping (making a ten) in detail
Regrouping in word problems means the story gives us a number of ones that pushes us past a ten. We have to trade ten ones for a new ten. Let's see how this looks in real life.
- Detroit Pizza Night: The Rodriguez family ordered a pizza with 64 pepperoni slices on top. They asked for extra cheese and 9 more pepperoni slices. How many pepperoni slices are on the pizza now? Think: 64 has 6 tens and 4 ones. 4 ones + 9 ones = 13 ones. That's 1 ten and 3 ones. So 6 tens + 1 ten = 7 tens, plus 3 ones = 73 pepperoni slices.
- Portland Farmers Market: Lena sold 57 jars of honey in the morning. In the afternoon, she sold 8 more jars. How many jars did she sell in all? 7 + 8 = 15 → 50 + 15 = 65 jars.
- Yellowstone National Park: A park ranger counted 73 bison in one field. 9 more bison walked over from the next valley. How many bison are in the field now? 3 + 9 = 12 → 70 + 12 = 82 bison.
Regrouping is like trading 10 pennies for 1 dime. You still have the same amount, but it looks different.
Using base-ten blocks to solve word problems
Base-ten blocks help us see what is happening in a word problem. Long rods are tens, and small cubes are ones. We can act out the story with blocks to understand regrouping.
- Brooklyn Classroom: Ms. Kelly's class has 38 glue sticks. The office sends 5 more. Show 38 with 3 rods and 8 cubes. Add 5 cubes. Now you have 13 cubes. Trade 10 cubes for 1 rod. Now you have 4 rods and 3 cubes = 43 glue sticks.
- San Diego Padres Game: Amir caught 46 foul balls (in his dream!). His friend gave him 8 more. 46 is 4 rods and 6 cubes. Add 8 cubes: 6+8=14 cubes. Trade 10 cubes for 1 rod: now 5 rods and 4 cubes = 54 foul balls.
If you don't have blocks, you can draw a line for each ten and a dot for each one. It works the same way.
Step-by-step guide to solve any word problem
A simple plan for word problems: 1) Read the whole story. 2) Find the two-digit number you start with. 3) Find how many ones to add. 4) Add the ones to the ones. 5) Regroup if needed. 6) Write the answer with a label.
- Story: At a powwow in New Mexico, there were 56 dancers in the circle. 7 more dancers joined them. How many dancers were there in all?
Step 1: Start with 56 (5 tens, 6 ones).
Step 2: Add 7 ones to 6 ones = 13 ones.
Step 3: 13 ones = 1 ten and 3 ones.
Step 4: 5 tens + 1 ten = 6 tens, plus 3 ones = 63.
Answer: 63 dancers.
Following the same steps every time makes word problems easier. Practice makes perfect.
Common mistakes and how to avoid them
Mistakes happen when we rush. Sometimes we add the ones to the tens by accident. Other times we forget to regroup. Let's learn from other students' errors.
- Mistake 1: "38 + 5 = 88" (a student added 5 to the tens). Fix: Remember, we only add ones to the ones place. 38 + 5 = 43.
- Mistake 2: "46 + 9 = 415" (a student wrote 15 ones without regrouping). Fix: 6+9=15. That's 1 ten and 5 ones. So 40+10+5=55.
- Mistake 3: "52 + 8 = 510" (confusing). Fix: 2+8=10, so 50+10=60. The answer is 60.
After you solve, ask: Is my answer close to the starting number? 52+8 should be around 60, not 500!
Practice reading word problems carefully
Sometimes word problems give extra details. You must find only the numbers that matter for the question. Ignore information that is not needed.
- Orlando Theme Park: At the roller coaster in Orlando, there were 84 people in line. The ride lasts 2 minutes. Then 7 more people joined the line. How many people are in line now? (Add 84 + 7 = 91. The 2 minutes is extra information and is not needed.)
- Austin Food Truck: A food truck in Austin had 65 tacos ready to sell. The truck also sells drinks for $3 each. Then the cook made 9 more tacos. How many tacos are there now? (Add 65 + 9 = 74. The $3 price is extra information and is not needed.)
Read the last sentence first. It tells you what to find. Then look back for the numbers you need.
Using number lines to add ones
A number line is a picture of numbers in order. You can start at the two-digit number and "jump" forward the number of ones you are adding. This helps you see regrouping.
- Boston Marathon: Runners have completed 37 miles. They need to run 4 more miles to finish. Start at 37. Jump 4 times: 38, 39, 40, 41. They finish at mile 41. (Notice you jumped past 40!)
- Nashville Music Store: The store sold 58 ukuleles last month. This month they sold 6 more. Start at 58. Jump: 59, 60, 61, 62, 63, 64. They sold 64 ukuleles all together.
A number line is like a ruler for numbers. You can draw one on scratch paper to help.
Real-life word problems from around the country
Math is everywhere! Here are real-life stories from different places and cultures. They show how we use adding every day.
- New Orleans Parade: Zydeco band had 26 musicians marching. 9 more musicians joined them. How many musicians are marching? 26 + 9 = 35 musicians.
- Alaska Fishing Trip: Kiana caught 47 salmon. Her uncle caught 8 more. How many salmon did they catch together? 47 + 8 = 55 salmon.
- Harlem Block Party: There were 83 people eating grilled food. 7 more people came with dishes to share. How many people are at the block party? 83 + 7 = 90 people.
- Silicon Valley Coding Club: 64 kids signed up for the coding club. 8 more kids joined the next day. How many kids are in the club? 64 + 8 = 72 kids.
Look for math in your own life: adding toys, snacks, or steps. You are a math detective!
Checking your answer makes sense
Always check your work. Does your answer seem right for the story? If you started with 42 and added 3, your answer should be around 45. If it's 82, something is wrong.
- Philadelphia Pretzels: 55 soft pretzels + 9 more = 64 pretzels. Check: 64 - 9 = 55, yes. Also, 55+10=65, so 55+9=64 is close to 65. Makes sense.
- Honolulu Surfboards: 37 surfboards + 6 more = 43 surfboards. Check: 37 is almost 40, add 6 is 46. Estimate of 46 is a little high, but close enough.
You can also add in a different order or use subtraction to check. 55+9=64, so 64-9 should be 55. If it is, you are correct.
Common Core alignment: CCSS.MATH.CONTENT.1.NBT.C.4 – Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
Notes for teachers
This lesson is aligned with CCSS.MATH.CONTENT.1.NBT.C.4. Use it for whole-class instruction, independent practice, or homework.
All content is 100% free, student-safe, and designed for classroom and home use. The study section now features richly detailed, word problems with clear step-by-step reasoning. Each section reinforces place value and the concept of regrouping in an age-appropriate manner.