## Common Core State Standards for Mathematics

Grade(s) 1 resources related to the following standard:
Operations and Algebraic Thinking
6. Add and subtract within 20, demonstrating fluency for addition and subtraction within 10. Use strategies such as counting on; making ten (e.g., 8 + 6 = 8 + 2 + 4 = 10 + 4 = 14); decomposing a number leading to a ten (e.g., 13 — 4 = 13 — 3 — 1 = 10 — 1 = 9); using the relationship between addition and subtraction (e.g., knowing that 8 + 4 = 12, one knows 12 — 8 = 4); and creating equivalent but easier or known sums (e.g., adding 6 + 7 by creating the known equivalent 6 + 6 + 1 = 12 + 1 = 13).

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This problems is an opportunity to explore triangular numbers in the familiar context of decorating a birthday cake with a number of candles corresponding to a child's age. The problem lends itself to systematic strategies and multiple representations. The Teachers' Notes page offers rationale, suggestions for implementation, discussion questions, and ideas for extension and support.
Activity
In this Illuminations lesson plan students explore the use of variables as they solve for the weights of objects using information presented in pictures. Learners model situations that involve adding and subtracting whole numbers, using objects, pictures, and symbols. A student activity sheet is available and downloadable (pdf).
Activity, Lesson Plans
In this 6-lesson unit, students explore 5 models of subtraction (counting, sets, number line, balanced equations, and inverse of addition) using connecting cubes. The lesson activities focus on the comparative mode of subtraction as children investigate the relationship between addition and subtraction, write story problems in which comparison is required, and practice the subtraction facts. The lessons include printable student activity sheets, a bibliography of children's counting books, questions for student discussion and teacher reflection, assessment options, extensions, and links to online applets (cataloged separately).
Activity, Lesson Plans, Unit of Instruction
This interactive 100 grid has a variety of open-ended uses. Users can "make" as many counters as they choose from among three different kinds, and then drag them onto the grid, allowing any number to be covered by up to 3 different markers at one time. An Ideas page offers possible tasks and games suited to the applet.
Activity, Interactive Media
Grade Level: K, 1, 2, 3, 4, 5
This iOS app, a prehistoric-themed game, was developed to help teach children to learn subitizing. The free game can be played by one or two players against the clock or not timed. Level one is only available to the user.
Activity, Interactive Media, Mobile App
This game from the BBC reinforces doubling and mental addition for a range of abilities. Students attempt to reach a target score by placing darts on the correct sections of a dartboard. The first level of the game provides practice doubling with a single number. Levels 2 and 3 increase the challenge level by involving two and three addends. Teachers and parents can control the starting level and the optional timing feature.
Game
Grade Level: K, 1, 2, 3
This interactive Flash applet models the difference meaning of subtraction. A child or teacher can compare two rows of beads and analyze the calculation they represent. Once a user sets up the two rows of beads (up to 30 each), the applet provides a series of animations which represents the rows with two number lines and then as a single number line with the difference indicated by a "jump". This applet works well with an interactive white board. A teacher's guide to this series of applets is cataloged separately.
Activity, Interactive Media