The Tens Digit - 1st Grade Math

1. Look at the number line. Point A shows a number that has the same number of tens as which other number?
   Answer: $82$ has the same tens Point A is at 80, which has 8 tens. The number 82 also has 8 tens (8 tens and 2 ones). Choice A has 2 tens, Choice C has 9 tens, and Choice D has 3 tens.
2. Look at the number 50. It is ____ tens and ____ ones.
   Answer: 5 tens and 0 ones When you see a two-digit number, each digit has a special job called its place value. The digit on the left tells you how many tens you have, and the digit on the right tells you how many ones. Think of tens as groups of 10 and ones as single leftover units. Look at 50. The digit on the left is 5, which sits in the tens place, so that means 5 tens. The digit on the right is 0, which sits in the ones place, so that means 0 ones. If you count 5 groups of ten, you get 10 + 10 + 10 + 10 + 10 = 50, which matches perfectly! So the answer is 5 tens and 0 ones. The choice "0 tens and 5 ones" flips the two digits around — that would actually spell the number 5, not 50. The choice "5 tens and 5 ones" adds an extra 5 ones, giving 50 + 5 = 55, which is too big. The choice "50 tens and 0 ones" confuses the whole number with the tens count — 50 tens would be 50 × 10 = 500, way too large. A helpful trick: for any two-digit number, just read it left to right. The first digit is your tens, and the second digit is your ones. Practice by covering one digit at a time and naming its place value — soon it will feel automatic!
3. Chen has 5 tens and 0 ones with ten-rods. What number is it?
   Answer: 50 This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 50 is 5 tens and 0 ones, which we can see by showing 5 ten-rods with no unit cubes; the digit in the tens place tells us how many tens, and the 0 in the ones place tells us there are no loose ones. The stimulus shows 50 represented with 5 ten-rods and no unit cubes. Choice D is correct because 50 is composed of 5 tens and 0 ones, shown by 5 ten-rods. Choice A is a common error where students think the 5 means 5 ones instead of tens (says 5 instead of 50); this happens because the 0 in ones place is sometimes overlooked and students miscount the number of tens shown. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (50 vs 55: both have 5 tens, but 55 also has 5 ones); write equations showing 5 tens + 0 ones = 50; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
4. Look at 80. How many ones are in 80?
   Answer: 0 This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 80 is 8 tens and 0 ones, which we can see by showing 8 ten-rods with no unit cubes; the digit in the tens place tells us how many tens, and the 0 in the ones place tells us there are no loose ones. The stimulus asks to look at 80 and identify how many ones are in it. Choice C is correct because 80 has exactly 0 ones, following the decade pattern. Choice A is a common error where students think the tens digit is the ones (says 8 ones); this happens because place value is abstract and students reverse tens and ones. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (80 vs 88: both have 8 tens, but 88 also has 8 ones); write equations showing 8 tens + 0 ones = 80; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
5. Keisha has 30 as 3 tens and 0 ones. How is 30 different from 35?
   Answer: 30 has 0 ones, but 35 has 5 ones This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 30 is 3 tens and 0 ones, while 35 is 3 tens and 5 ones; the digit in the tens place tells us how many tens, and the ones place differs by having 0 or more. The stimulus shows 30 represented with 3 ten-rods and no unit cubes, compared to 35. Choice B is correct because 30 has 0 ones, but 35 has 5 ones, highlighting the key difference in the ones place. Choice A is a common error where students reverse the ones for each number (says 30 has 3 ones and 35 has 0); this happens because place value is abstract and students overlook the 0 in ones place for decades. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (30 vs 35: both have 3 tens, but 35 also has 5 ones); write equations showing 3 tens + 0 ones = 30 vs 3 tens + 5 ones = 35; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
6. Look at 40 shown as 4 ten-rods and 0 ones. 40 is ____ tens and ____ ones.
   Answer: 4 tens and 0 ones When you work with two-digit numbers, think of them as groups: each ten-rod stands for a bundle of 10, and each ones cube stands for a single 1. The number tells you how many bundles of ten and how many leftover ones you have. Here you can see 4 ten-rods and 0 ones cubes. Counting the tens gives 4 × 10 = 40, and there are no extra ones to add. So 40 is made of 4 tens and 0 ones — exactly what the picture shows. Now look at why the other choices don't fit. "0 tens and 4 ones" flips the picture backwards; that would only make 4, not 40. "4 tens and 4 ones" adds four extra ones that aren't in the picture, giving 44 instead of 40. "40 tens and 0 ones" confuses the whole number with the number of tens — but 40 tens would actually be 40 × 10 = 400, way too big. A helpful trick: in a two-digit number, the first digit tells you the tens and the second digit tells you the ones. In 40, the 4 is in the tens place and the 0 is in the ones place, so it must be 4 tens and 0 ones. Whenever you see ten-rods, just count the rods for tens and the loose cubes for ones.
7. Jamal shows 2 ten-rods and 0 ones. What number is it?
   Answer: 20 This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 20 is 2 tens and 0 ones, which we can see by showing 2 ten-rods with no unit cubes; the digit in the tens place tells us how many tens, and the 0 in the ones place tells us there are no loose ones. The stimulus describes Jamal showing 2 ten-rods and 0 ones, representing a decade number. Choice C is correct because 20 is composed of 2 tens and 0 ones, shown by 2 ten-rods. Choice A is a common error where students count only the number of tens without considering place value, thinking it's just 2 instead of 20; this happens because place value is abstract and the 0 in ones place is sometimes overlooked. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (20 vs 22: both have 2 tens, but 22 also has 2 ones); write equations showing 2 tens + 0 ones = 20; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
8. What do 10, 20, and 30 have in common?
   Answer: They all have 0 ones This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 10 is 1 ten and 0 ones, 20 is 2 tens and 0 ones, and 30 is 3 tens and 0 ones; we can see this by showing ten-rods with no unit cubes, where the tens digit varies but ones is always 0. The stimulus asks what 10, 20, and 30 have in common. Choice B is correct because they all have 0 ones, a key feature of decade numbers. Choice A is a common error where students focus on one number's tens (3 tens for 30) instead of the shared trait; this happens because the 0 in ones place is sometimes overlooked. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (30 vs 33: both have 3 tens, but 33 also has 3 ones); write equations showing varying tens + 0 ones = decade; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
9. Maya shows 9 ten-rods and 0 ones. What number is shown?
   Answer: 90 This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 90 is 9 tens and 0 ones, which we can see by showing 9 ten-rods with no unit cubes; the digit in the tens place tells us how many tens, and the 0 in the ones place tells us there are no loose ones. The stimulus describes Maya showing 9 ten-rods and 0 ones, and asks what number is shown. Choice A is correct because 90 is composed of 9 tens and 0 ones, shown by 9 ten-rods. Choice C is a common error where students confuse decade structure with teen structure (1 ten and 9 ones for 19); this happens because decade numbers look similar to teens but have different structure. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (90 vs 99: both have 9 tens, but 99 also has 9 ones); write equations showing 9 tens + 0 ones = 90; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
10. Sofia has 30 as 3 bundles of 10 and 0 loose sticks. How many ones?
    Answer: 0 This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 30 is 3 tens and 0 ones, which we can see by showing 3 bundles of 10 sticks with no loose sticks; the digit in the tens place tells us how many tens, and the 0 in the ones place tells us there are no loose ones. The stimulus shows 30 represented with 3 bundles of 10 sticks and no loose sticks. Choice C is correct because 30 is composed of 3 tens and 0 ones, shown by 3 bundles. Choice A is a common error where students reverse tens and ones (think 3 ones instead of 0); this happens because the 0 in ones place is sometimes overlooked and students confuse decade structure with teen structure. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (30 vs 33: both have 3 tens, but 33 also has 3 ones); write equations showing $3 \text{ tens} + 0 \text{ ones} = 30$; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
11. Maria has some tens blocks and ones blocks. She makes the number $70$. Then she trades $2$ tens blocks for $20$ ones blocks. How many tens blocks does she have now?
    Answer: $5$ tens blocks To make 70, Maria needs 7 tens blocks (and 0 ones blocks). When she trades 2 tens blocks for 20 ones blocks, she has 7 - 2 = 5 tens blocks remaining. Choice B incorrectly keeps the original number of tens. Choice C incorrectly adds instead of subtracts. Choice D shows only the number traded away.
12. Maya has 4 bundles of 10 straws and 0 loose straws. What number do the bundles represent?
    Answer: 40 4 bundles of 10 straws make 40, since 4 tens equal 40. 4 counts only the number of bundles, not the value they represent. 44 mistakenly adds 4 loose straws that Maya doesn't have. 30 would only be 3 bundles of 10, not 4. Only 40 correctly matches 4 bundles of 10 with none left over.
13. Chen has 3 tens and 0 ones. What number is it?
    Answer: 30 3 tens and 0 ones makes the number 30. 13 mixes up the order of the tens and ones digits. 33 adds an extra 3 in the ones place that isn't there. 3 counts only the number of tens groups, not the value they represent. Only 30 correctly shows the number made from 3 tens and 0 ones.
14. Jamal shows 60 with 6 ten-rods and 0 ones. How many tens are in 60?
    Answer: 6 This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 60 is 6 tens and 0 ones, which we can see by showing 6 ten-rods with no unit cubes; the digit in the tens place tells us how many tens, and the 0 in the ones place tells us there are no loose ones. The stimulus shows 60 represented with 6 ten-rods and no unit cubes. Choice A is correct because 60 contains exactly 6 tens with 0 ones. Choice C is a common error where students count the total value instead of number of tens (says 60 = 60 tens); this happens because place value is abstract and students confuse the total count with the number of tens. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (60 vs 66: both have 6 tens, but 66 also has 6 ones); write equations showing 6 tens + 0 ones = 60; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.
15. Look at the pattern: $20, 30, 40, 50$. The tens in these numbers are $2, 3, 4, 5$. If the pattern continues for two more numbers, how many tens will the last number have?
    Answer: The last number will have $7$ tens The pattern of tens is 2, 3, 4, 5, and continues 6, 7. So the last number after two more steps will have 7 tens (which would be the number 70). Choice A gives the second-to-last number of tens. Choices C and D confuse the number of tens with the actual number value.
16. Tom picks a number between $40$ and $80$. His number has exactly $5$ tens. Then he adds $10$ to his number. How many tens does his new number have?
    Answer: $6$ Tom's number has 5 tens, and adding 10 adds one more ten, giving 6 tens. 5 tens repeats his starting number without adding the new ten. 15 tens is far more than adding just one ten would give. 10 tens mixes up the amount added with the total number of tens. Only 6 tens correctly shows one more ten than Tom started with.
17. Lily has $90$ stickers arranged in groups of ten. She gives away $30$ stickers to her friends. How many groups of ten does she have left?
    Answer: $6$ Lily starts with 9 groups of ten and gives away 3 groups of ten, leaving 6 groups. 3 is how many groups she gave away, not how many she has left. 9 repeats her starting number of groups without subtracting any. 60 mixes up the number of stickers with the number of groups. Only 6 correctly shows how many groups of ten Lily has left.
18. Jake writes a number that has $4$ tens. Emma writes a number that has $2$ more tens than Jake's number. What could be Emma's number?
    Answer: Emma could write $60$ Jake's number has 4 tens, and 2 more tens than that is 6 tens, which is 60. 20 would mean Emma had 2 fewer tens than Jake instead of 2 more. 80 would mean Emma doubled Jake's tens instead of adding 2 more. 42 mixes up tens and ones by adding the 2 as ones instead of tens. Only 60 correctly shows 2 more tens than Jake's 4 tens.
19. Use the chart to answer the question. Which two numbers from the chart have a total of $7$ tens when you add their tens together?
    Answer: $20$ and $50$ have $7$ tens total Looking at the tens in each number: 20 has 2 tens, 50 has 5 tens, and 2 + 5 = 7 tens total. Choice A: 3 + 4 = 7 tens but 40 is not in the chart. Choice C: 6 + 1 = 7 tens but 60 is not in the chart. Choice D: 4 + 2 = 6 tens, not 7.
20. Maya has 70 as 7 bundles of 10 and 0 loose ones. 70 is how many tens?
    Answer: 7 This question tests 1st grade understanding that decade numbers (10, 20, 30...90) represent multiples of ten with 0 ones (CCSS.1.NBT.2.c). Decade numbers—10, 20, 30, 40, 50, 60, 70, 80, and 90—are special because they contain only tens and no ones. For example, 70 is 7 tens and 0 ones, which we can see by showing 7 bundles of 10 sticks with no loose sticks; the digit in the tens place tells us how many tens, and the 0 in the ones place tells us there are no loose ones. The stimulus shows 70 represented with 7 bundles of 10 sticks and no loose sticks. Choice B is correct because 70 is composed of 7 tens and 0 ones, shown by 7 bundles. Choice C is a common error where students count the total value instead of number of tens (says 70 = 70 tens); this happens because place value is abstract and students confuse the total count with the number of tens. To help students: Use base-10 blocks extensively—show only ten-rods with explicit empty space where ones would be; emphasize 0 ones verbally and visually; practice counting by tens (10, 20, 30...90); connect decade numbers to skip counting; compare decades to non-decades (70 vs 77: both have 7 tens, but 77 also has 7 ones); write equations showing 7 tens + 0 ones = 70; use place value charts highlighting the 0 in ones place; have students build each decade with blocks.

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