This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition, where instead of taking away, we ask what number added to the subtrahend equals the minuend. For example, to solve 10 - 3, we can think '3 plus what equals 10?' or write it as 3 + ? = 10, and the missing addend 7 is the difference. The problem states that 20 - 14 = ? is the same as 14 + ? = 20 and asks for the number that goes in the ?. Choice C is correct because when we add 6 to 14, we get 20, so 14 + 6 = 20, which means 20 - 14 = 6. Choice A is a common error where students might make an off-by-one mistake, such as counting from 14 to 20 as 7 instead of 6, because counting on accurately requires practice. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at 14, count forward to 20); teach fact families explicitly (14+6=20, 6+14=20, 20-14=6, 20-6=14); use 'think addition' language consistently ('to subtract 20-14, think what plus 14 equals 20'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition. Instead of 'taking away,' we can ask 'what do I add to get to the total?' For example, to solve 10 - 8, we can think '8 plus what equals 10?' or write it as 8 + ? = 10. Finding the missing addend (2) gives us the answer to the subtraction problem. This strategy is often easier than counting back, especially when the numbers are close together. The problem presents the subtraction 12-9 and equates it to the unknown addend equation 9 + ? = 12, asking for the missing number. Choice B is correct because when we add 3 to 9, we get 12, so 9 + 3 = 12, which means 12 - 9 = 3. Choice C is a common error where students add the two numbers instead of finding the difference, getting 21, because the connection between addition and subtraction is abstract. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at smaller number, count forward to larger); teach fact families explicitly (9+3=12, 3+9=12, 12-9=3, 12-3=9); use 'think addition' language consistently ('to subtract 12-9, think what plus 9 equals 12'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition, where instead of taking away, we ask what number added to the subtrahend equals the minuend. For example, to solve 10 - 3, we can think '3 plus what equals 10?' or write it as 3 + ? = 10, and the missing addend 7 is the difference. The problem states that 18 - 13 = ? is the same as 13 + ? = 18 and asks for the missing number. Choice B is correct because when we add 5 to 13, we get 18, so 13 + 5 = 18, which means 18 - 13 = 5. Choice A is a common error where students might make an off-by-one mistake, such as counting from 13 to 18 as 6 instead of 5, because the connection between addition and subtraction is abstract. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at 13, count forward to 18); teach fact families explicitly (13+5=18, 5+13=18, 18-13=5, 18-5=13); use 'think addition' language consistently ('to subtract 18-13, think what plus 13 equals 18'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition. Instead of 'taking away,' we can ask 'what do I add to get to the total?' For example, to solve 10 - 8, we can think '8 plus what equals 10?' or write it as 8 + ? = 10. Finding the missing addend (2) gives us the answer to the subtraction problem. This strategy is often easier than counting back, especially when the numbers are close together. The problem presents the subtraction 15-8 and suggests thinking of it as the unknown addend equation 8 + ? = 15, asking for the missing number. Choice A is correct because when we add 7 to 8, we get 15, so 8 + 7 = 15, which means 15 - 8 = 7. Choice B is a common error where students add the two numbers instead of finding the difference, getting 23, because they may be more familiar with the 'taking away' model of subtraction. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at smaller number, count forward to larger); teach fact families explicitly (8+7=15, 7+8=15, 15-8=7, 15-7=8); use 'think addition' language consistently ('to subtract 15-8, think what plus 8 equals 15'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition. Instead of 'taking away,' we can ask 'what do I add to get to the total?' For example, to solve 10 - 8, we can think '8 plus what equals 10?' or write it as 8 + ? = 10. Finding the missing addend (2) gives us the answer to the subtraction problem. This strategy is often easier than counting back, especially when the numbers are close together. The problem is a word problem: Maya has 6 stickers and asks how many more are needed to have 14, which is equivalent to 14 - 6 or 6 + ? = 14. Choice A is correct because when we add 8 to 6, we get 14, so 6 + 8 = 14, which means 14 - 6 = 8. Choice D is a common error where students add the two numbers instead of finding the difference, getting 20, because counting on accurately requires practice. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at smaller number, count forward to larger); teach fact families explicitly (6+8=14, 8+6=14, 14-6=8, 14-8=6); use 'think addition' language consistently ('to find how many more, think what plus 6 equals 14'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition, where instead of taking away, we ask what number added to the subtrahend equals the minuend. For example, to solve 10 - 3, we can think '3 plus what equals 10?' or write it as 3 + ? = 10, and the missing addend 7 is the difference. The problem asks to subtract 16 - 7 by thinking of it as 7 + ? = 16 and finding the answer. Choice C is correct because when we add 9 to 7, we get 16, so 7 + 9 = 16, which means 16 - 7 = 9. Choice B is a common error where students might count incorrectly when counting on, such as making an off-by-one error by thinking from 7 to 16 is 8 steps instead of 9, because the unknown addend representation is less familiar and requires practice. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at 7, count forward to 16); teach fact families explicitly (7+9=16, 9+7=16, 16-7=9, 16-9=7); use 'think addition' language consistently ('to subtract 16-7, think what plus 7 equals 16'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition, where instead of 'taking away,' we ask 'what do I add to get to the total?' For example, to solve $10 - 3$, we can think '3 plus what equals 10?' or write it as $3 + ? = 10$, and finding the missing addend (7) gives the subtraction answer. This strategy leverages the inverse relationship between addition and subtraction, making it easier for young learners to use known addition facts. The problem uses a context where Chen has 9 marbles and asks how many more to have 16, equivalent to $16 - 9 = ?$. Choice B (7) is correct because when we add 7 to 9, we get 16, so $9 + 7 = 16$, which means $16 - 9 = 7$. Choice A (8) is a common error where students make an off-by-one mistake, such as counting from 9 to 16 as eight steps instead of seven, which happens because counting on accurately requires practice. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at smaller number, count forward to larger); teach fact families explicitly ($9+7=16$, $7+9=16$, $16-9=7$, $16-7=9$); use 'think addition' language consistently ('to subtract $16-9$, think what plus 9 equals 16'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition, where instead of taking away, we ask what number added to the subtrahend equals the minuend. For example, to solve 10 - 3, we can think '3 plus what equals 10?' or write it as 3 + ? = 10, and the missing addend 7 is the difference. The problem asks to find 12 - 10 by solving 10 + ? = 12 and identifying the missing number. Choice B is correct because when we add 2 to 10, we get 12, so 10 + 2 = 12, which means 12 - 10 = 2. Choice A is a common error where students might include the starting number when counting, such as counting 10, 11, 12 as 3 instead of 2, because counting on accurately requires practice. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at 10, count forward to 12); teach fact families explicitly (10+2=12, 2+10=12, 12-10=2, 12-2=10); use 'think addition' language consistently ('to subtract 12-10, think what plus 10 equals 12'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition, where instead of 'taking away,' we ask 'what do I add to get to the total?' For example, to solve 10 - 3, we can think '3 plus what equals 10?' or write it as 3 + ? = 10, and finding the missing addend (7) gives the subtraction answer. This strategy leverages the inverse relationship between addition and subtraction, making it easier for young learners to use known addition facts. The problem presents 18 - 10 = ? and suggests thinking 10 + ? = 18, asking for the missing number. Choice A (8) is correct because when we add 8 to 10, we get 18, so 10 + 8 = 18, which means 18 - 10 = 8. Choice C (7) is a common error where students make an off-by-one error, such as counting from 10 to 18 as seven steps instead of eight, which happens because they might include the starting number when counting. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at smaller number, count forward to larger); teach fact families explicitly (10+8=18, 8+10=18, 18-10=8, 18-8=10); use 'think addition' language consistently ('to subtract 18-10, think what plus 10 equals 18'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.

This question tests 1st grade understanding of subtraction as an unknown-addend problem (CCSS.1.OA.4). Subtraction can be solved by thinking about addition. Instead of 'taking away,' we can ask 'what do I add to get to the total?' For example, to solve $10 - 8$, we can think '8 plus what equals 10?' or write it as $8 + ? = 10$. Finding the missing addend (2) gives us the answer to the subtraction problem. This strategy is often easier than counting back, especially when the numbers are close together. The problem presents the subtraction $9-4$ and suggests thinking of it as the unknown addend equation $4 + ? = 9$, asking for the answer. Choice D is correct because when we add 5 to 4, we get 9, so $4 + 5 = 9$, which means $9 - 4 = 5$. Choice B is a common error where students add the two numbers instead of finding the difference, getting 13, because the unknown addend representation is less familiar. To help students: Use part-part-whole diagrams showing the relationship; practice on number lines with counting-on (start at smaller number, count forward to larger); teach fact families explicitly ($4+5=9$, $5+4=9$, $9-4=5$, $9-5=4$); use 'think addition' language consistently ('to subtract $9-4$, think what plus 4 equals 9'); provide many examples connecting subtraction to unknown addend; emphasize that this strategy is especially useful when numbers are close together; use context problems where 'how many more needed' feels natural; practice writing both forms of the problem.