This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to find pairs that make 10 (like 7+3), add first, then the third; doubles or easy adds work too, with flexible ordering. The story presents three quantities: 7 marbles from Keisha, 3 from Carlos, and 6 from Yuki. Choice C is correct because adding all three gives 7 + 3 + 6 = 16; we can add 7+3=10 first, then 10+6=16. Choice D is a common error from misadding after pairing, like 10+4=14 instead of 6; this stems from non-automatic facts or distraction. To help students: Use marble bags for groups; teach making-10 explicitly; model with parentheses (7+3)+6; connect to sharing games; have students practice and explain.

This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for two numbers that make 10 (like 4+6), add those first, then the third number; another is to add in any order using commutative and associative properties. The story presents three quantities: 4 points in round 1, 6 points in round 2, and 5 points in round 3. Choice C is correct because adding all three numbers gives 4 + 6 + 5 = 15; for example, add 4+6=10 first, then 10+5=15. Choice A is a common error where students only add two numbers, like 4+6=10 and forget the 5; this happens because keeping track of three numbers is challenging and applying strategies requires practice. To help students: Use physical objects in three groups that students can count and combine; teach making-10 strategy explicitly with pairs that sum to 10; practice doubles facts; model different groupings using parentheses like (4+6)+5; use visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy; connect to real contexts with three groups.

This question tests 1st grade ability to add three whole numbers with $sum \leq 20$ (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for two numbers that make 10 (like $6+4$ or $7+3$), add those first, then add the third number; another strategy is to look for doubles (like $4+4$) or numbers that are easy to add together, combine those first, then add the remaining number; students can add in any order because of the commutative and associative properties. The story presents three quantities: 7 cookies after lunch, 3 cookies after snack, and 2 cookies after dinner. Choice B is correct because adding all three numbers gives $7 + 3 + 2 = 12$; we can add $7+3=10$ first, then $10+2=12$. Choice A is a common error where students only add two of the three numbers, such as $7+3=10$, and forget to add the third; this happens because keeping track of three numbers is challenging. To help students: Use physical objects in three groups that students can count and combine; teach making-10 strategy explicitly with pairs that sum to 10; practice doubles facts ($3+3$, $4+4$, $5+5$); model different groupings using parentheses: ($7+3)+2$ or $7+(3+2)$; use visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy; practice with various number combinations; connect to real contexts with three groups.

This question tests 1st grade ability to add three whole numbers with sum $≤20$ (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for two numbers that make 10 (like $6+4$ or $7+3$), add those first, then add the third number; another strategy is to look for doubles (like $4+4$) or numbers that are easy to add together, combine those first, then add the remaining number; students can add in any order because of the commutative and associative properties. The story presents three quantities: 1 cookie at breakfast, 8 cookies at lunch, and 6 cookies at dinner. Choice B is correct because adding all three numbers gives $1 + 8 + 6 = 15$; we can add $1+8=9$ first, then $9+6=15$, or group $8+6=14$ and $14+1=15$. Choice A is a common error where students only add two of the three numbers, such as $8+6=14$ and forgetting the 1, or make a calculation error like $1+8=9$ and $9+5=14$ by miscounting the 6; this happens because students may focus on two numbers and lose track of the third. To help students: Use physical objects in three groups that students can count and combine; teach making-10 strategy explicitly with pairs that sum to 10; practice doubles facts ($3+3$, $4+4$, $5+5$); model different groupings using parentheses: ($(1+8)+6$ or $1+(8+6)$); use visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy; practice with various number combinations; connect to real contexts with three groups.

This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for two numbers that make 10 (like $6+4$ or $7+3$), add those first, then add the third number; another is to look for doubles or easy pairs, and students can add in any order due to commutative and associative properties. The story presents three quantities: 6 red stickers, 4 blue stickers, and 3 green stickers. Choice C is correct because adding all three numbers gives $6 + 4 + 3 = 13$; we can add $6+4=10$ first, then $10+3=13$. Choice A is a common error where students only add two of the three numbers, like $6+4=10$, forgetting the third; this happens because keeping track of three numbers is challenging for young learners. To help students: Use physical objects in three groups that they can count and combine; teach the making-10 strategy explicitly with pairs that sum to 10; practice with visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy.

This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to identify doubles (like $5+5$), add them first, then the third; grouping helps, and addition is commutative and associative. The story presents three quantities: 5 apples in a basket, 5 on the table, and 4 on the counter. Choice A is correct because adding all three gives $5 + 5 + 4 = 14$; we can add the doubles $5+5=10$, then $10+4=14$. Choice B is a common error where students only add two numbers, like $5+5=10$, forgetting the third; this is due to challenges in tracking multiple addends. To help students: Use fruit manipulatives in groups; teach doubles explicitly; demonstrate groupings like $(5+5)+4$; use pictures of locations; practice with similar problems and discuss errors.

This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for doubles (like 6+6), add those first, then the third number; another is to make 10 with pairs (like 6+4) and use commutative and associative properties. The story presents three quantities: 6 stickers on Monday, 4 stickers on Tuesday, and 6 stickers on Wednesday. Choice A is correct because adding all three numbers gives 6 + 4 + 6 = 16; for example, add 6+4=10 first, then 10+6=16, or add the doubles 6+6=12 then 12+4=16. Choice B is a common error where students add only two numbers, like 6+6=12 and forget the 4; this happens because keeping track of three numbers is challenging and students may focus on two. To help students: Use physical objects in three groups that students can count and combine; teach doubles facts explicitly (6+6=12); practice making-10 strategy; model different groupings using parentheses like (6+6)+4; use visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy; connect to real contexts with three groups.

This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for two numbers that make 10 (like 6+4 or 7+3), add those first, then add the third number; another strategy is to look for doubles (like 4+4) or numbers that are easy to add together, combine those first, then add the remaining number; students can add in any order because of the commutative and associative properties. The story presents three quantities: 6 shells at the beach, 4 shells by the rocks, and 5 shells near the sand. Choice B is correct because adding all three numbers gives 6 + 4 + 5 = 15; we can add 6+4=10 first, then 10+5=15. Choice C is a common error where students make a calculation error, such as 6+4=10 and 10+6=16 by mistakenly using 6 instead of 5, or try to use a strategy but apply it incorrectly; this happens because keeping track of three numbers is challenging and students may focus on two numbers and lose track of the third. To help students: Use physical objects in three groups that students can count and combine; teach making-10 strategy explicitly with pairs that sum to 10; practice doubles facts (3+3, 4+4, 5+5); model different groupings using parentheses: (6+4)+5 or 6+(4+5); use visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy; practice with various number combinations; connect to real contexts with three groups.

This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for two numbers that make 10 (like 6+4 or 7+3), add those first, then add the third number; another strategy is to look for doubles (like 4+4) or numbers that are easy to add together, combine those first, then add the remaining number; students can add in any order because of the commutative and associative properties. The story presents three quantities: 9 toys in a bin, 1 toy on the bed, and 7 toys on a shelf. Choice A is correct because adding all three numbers gives 9 + 1 + 7 = 17; we can add 9+1=10 first, then 10+7=17. Choice B is a common error where students make a calculation error, such as 9+7=16 and forgetting the 1, or try to use a strategy but apply it incorrectly like misidentifying pairs that make 10; this happens because keeping track of three numbers is challenging and students may focus on two numbers and lose track of the third. To help students: Use physical objects in three groups that students can count and combine; teach making-10 strategy explicitly with pairs that sum to 10; practice doubles facts (3+3, 4+4, 5+5); model different groupings using parentheses: (9+1)+7 or 9+(1+7); use visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy; practice with various number combinations; connect to real contexts with three groups.

This question tests 1st grade ability to add three whole numbers with sum ≤20 (CCSS.1.OA.2). When adding three numbers, students can use helpful strategies to make it easier. One strategy is to look for two numbers that make 10 (like 7+3), add those first, then the third number; another is to add in any order using commutative and associative properties. The story presents three quantities: 7 apples in a basket, 3 apples on the table, and 4 apples on the counter. Choice A is correct because adding all three numbers gives 7 + 3 + 4 = 14; for example, add 7+3=10 first, then 10+4=14. Choice B is a common error where students only add two numbers, like 7+3=10 and forget the 4; this happens because calculation facts may not be automatic and applying strategies requires practice. To help students: Use physical objects in three groups that students can count and combine; teach making-10 strategy explicitly with pairs that sum to 10; practice doubles facts; model different groupings using parentheses like (7+3)+4; use visual representations showing three groups; emphasize that order doesn't matter; have students explain their strategy; connect to real contexts with three groups.