Common Core: 1st Grade Math : Adding and Subtracting Within 20

Study concepts, example questions & explanations for Common Core: 1st Grade Math

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Example Questions

Example Question #853 : Operations & Algebraic Thinking

Jenny has  games. She let her friend use  of them for her birthday part. How many does Jenny have left?

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because we want to know how many games Jenny has left after she gives some to her friend. We take the total number of games that Jenny has, and then we subtract the number that she gave to her friend. .

Example Question #853 : Operations & Algebraic Thinking

Sarah got  birthday gifts for her birthday. She’s opened  of them. How many does she have left to open? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because we want to know how many gifts she has left to open after she’s already opened some of her gifts. We take the total number of gifts she has, and then we subtract the number of gifts that she’s opened. .

Example Question #851 : Operations & Algebraic Thinking

Matt invited  of his friends to a cookout. of his friends did not come. How many of his friends did come to his cookout? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because we want to find out how many of Matt’s invited friends were able to come to his party. We take the total number of people that were invited, and subtract the number of people that did not come. 

Example Question #861 : Operations & Algebraic Thinking

Ms. Smith’s class has  students.  of her students are out with the flu today. How many students are in the class today? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because we want to know how many students in Ms. Smith’s class are in school today out of the total number of students that she has. We take the total number of students and subtract the number of students who are not in school today. .

Example Question #862 : Operations & Algebraic Thinking

Joe has  total math problems to complete for homework this week. He wants to get  done today. How many will he have left after today? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because we want to know how many homework problems Joe will have left after he completes some of them. We take the total number of problems that he has and subtract the number that he plans to do tonight. 

Example Question #863 : Operations & Algebraic Thinking

Lisa has  birthday parties to go to this year. She has already gone to  of them. How many parties does she have left to go to this year? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because we want to know how many birthday parties Lisa has left to attend this year. We take the total number of parties that she is invited to, and subtract the number of parties that she has already been to. 

Example Question #461 : Adding And Subtracting Within 20

Mr. Bell has  desks in his classroom, but he only needs  desks because he has  students. How many extra desks does he have? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because we want to know how many desks are left over after all of Mr. Bell’s class sits at a desk. We take the number of desks in his room, and subtract the number of students that he has. 

Example Question #861 : Operations & Algebraic Thinking

Tom went to school with  pieces of gum. He left school with  pieces. How many pieces did he chew at school? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because Tim's total amount of gum decreased. 

We can start at  and count back .

Example Question #862 : Operations & Algebraic Thinking

 Tiffany bought  balloons. On the way to the car,  blew away. How many does she have left? 

Possible Answers:

Correct answer:

Explanation:

This is a subtraction problem because Tiffany lost balloons so she will have less than what she started with. 

We can start at  and count back .

Example Question #1 : Knowing How And When To Subtract

Possible Answers:

Correct answer:

Explanation:

To subtract we can count backwards. Start at  and count back 

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