# 2nd Grade Computation and Algebraic Thinking Resources

## Add and Subtract 1 and 10

This is meant to develop understanding of addition and subtraction of 1 and 10. You are given a starting number and and ending number (the relationship between having been determined by the adjustable "Difficulty"). Your job is to get to the ending number by adding or subtracting one(s) or ten(s). Choose a representation to help your thinking and try to find the most efficient pathway.

What are the missing digits of this equation? Think strategically about the possibilities, then click the buttons to find out. Play this game slowly with lots of conversations about what you know/don't know. See this Marilyn Burns blog post for more information and instructional ideas.

## Balance (The Farmer's Stone)

There's a sack on a scale. How much does it weigh? Use the weights to find out and explore flexible approaches to equality.

## Balanced Expressions

Explore notions of equality and inequality by dragging expressions to the balance. Select whether you'd like your inequalities recorded with the "not equal" sign (â‰ ) or greater/less than signs (> and <).

## Close to 1000

Arrange the digits 1-9 into three 3-digit numbers. Try to get the sum as close to 1000 as possible.

## Commuting Counters

Enter two addends, then click next. The addends will show up as counters. Keep clicking next to see the commutative property in action.

## Five by Five

A 2-player, GeoGebra version of Sara VanDerWerf's game. You will place (up to) 25 numbers in the grid. You score by placing (by clicking) matching numbers in adjacent squares. Decide whether you want to play a timed or untimed game, and whether you'd like the scores to be calculated by sums or products. See Sara's blog post for more information.

## Move the Number

This activity is meant to develop flexible, creative thinking about numbers and operations. Your goal is to move a from a starting number to a target number, but there are many ways to do this! Adjust the sliders to control the bounds of the numbers involved.

## Number Balance

Explore ideas around equality, decomposition, missing addends, and more! Up the ante by finding the mystery number.

## Part-Part-Whole Estimation

Adjust the slider to control the size of the numbers. One of the pieces (a part or the whole) is randomly provided. Use estimation to fill in the rest. Feedback provided.

## Part-Whole Rectangles

Designed to develop ability to estimate reasonable answers in subtraction situations. Specify your own subtraction problem (or generate a random one), then represent the relative size of the subtrahend by shading a rectangle representing the minuend. Feedback on accuracy of shading is provided. (Not included but recommended: finish by estimate the size of the difference before actually doing the subtraction.)

## Subtraction on Number Line

Designed to develop a specific strategy when faced with a regrouping problem in subtraction. Specify a subtraction problem, then see that represented on the number line as the distance between the two numbers. Since that is a fixed distance, explore how it can be found by adjusting the minuend and subtrahend to generate equivalent subtraction problems, some which would not require regrouping.

## Sums to 100

This Open Middle task is designed to get students thinking flexibly about using place value in addition. Arrange the digits to create three 2-digit numbers. Use trial and error to get your sum as close to 100 as possible. Can you get it to be exactly 100?